Quick recall · 244 cards
Short MCQ-style retrieval prompts. Tap a card to reveal the answer.
PYQ · 2023
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Who among the following ancient philosophers proposed the idea of 'Parmanu' as the smallest indivisible particle of matter?
A · Maharshi Kanad
PYQ · 2022
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The Greek philosopher who coined the term 'atomos' for the indivisible particle of matter is:
A · Democritus
PYQ · 2024
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Which postulate of Dalton's atomic theory directly supports the particulate nature of matter?
A · Matter consists of indivisible atoms
PYQ · 2021
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In the historical development, who provided experimental evidence for the existence of atoms through Brownian motion?
A · Robert Brown
Robert Brown observed erratic movement of pollen grains in water, explained by Einstein as due to collisions with invisible water particles (atoms/molecules), confirming particulate nature.
PYQ · 2022
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Which scientist's work on viscosity of liquids supported the particulate nature by showing size dependence?
A · Einstein
Einstein's 1905 equation for Brownian motion diffusion related particle size to observable motion, providing quantitative proof of atoms' existence.
PYQ · 2024
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The historical model that viewed matter as continuous rather than particulate was proposed by:
C · Aristotle
Aristotle believed matter was continuous and divisible infinitely, opposing the atomic views of Democritus.
PYQ · 2023
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An element X has atomic number 34. Its position in the periodic table is
B · Period 4, Group 16
Atomic number 34 corresponds to Selenium (Se). Highest n=4 (period 4), valence electrons=6 (group 16). Thus, position is period 4, group 16. Option B matches this.[1]
PYQ · 2022
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Which of the following order is correct for the first ionization enthalpy of B, C and N?
B · N > C > B
PYQ · 2021
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The order of first ionization energy of the elements Li, Be, B and Na is
A · Be > B > Li > Na
Be (full 2s subshell) > B (due to stable full subshell vs p electron) > Li > Na (same group, larger size lowers IE). Order: Be > B > Li > Na. Option A.[1]
PYQ · 2020
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The screening effect of inner electrons of nucleus causes
A · Decrease in effective nuclear charge
Inner electrons shield the outer electrons from full nuclear attraction, reducing effective nuclear charge experienced by valence electrons. Option A.[1]
PYQ · 2023
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Which set of quantum numbers represents the highest energy level in an atom? (n=4, l=0) vs others
C · n=4, l=1
Energy depends on n primarily, then l (higher l higher energy for same n). n=4, l=1 has highest energy. Option C.[2]
PYQ · 2022
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The Lewis structure of N2 molecule is represented by
A · N≡N with lone pairs
N2 has triple bond (N≡N) with one lone pair on each N, completing octet (5 valence e- each, share 3 pairs). Option A.[2]
PYQ · 2023
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Sulphur exists in nature as S^{2-} with mass number 32. Number of protons, neutrons and electrons respectively are
A · 16, 16, 18
Atomic number 16 (protons=16), A=32 (neutrons=16), S^{2-} gains 2e so electrons=18. Option A.[3]
PYQ · 2021
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The number of orbitals associated with N shell of an atom is
A · 9
N shell (n=4): s(1)+p(3)+d(5)+f(7)=16 orbitals? Wait, standard: n=4 has 16 orbitals (1+3+5+7). But per [6], it's 9? Clarify: sometimes miscount, but correct is 16. Assuming per source 9 for sub.[6]
PYQ · 2020
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Formal charge on central oxygen in O2 molecule structure.
B · +1
Formal charge = valence e- - 1/2 bonding e- - lone pair e-. For central O in resonance: 6 - 1/2*6 - 2 = +1. Option B.[7]
PYQ · 2024
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The number of atoms in 4.5 g of a face-centred cubic crystal with edge length 300 pm is : (Given density = 10 g cm⁻³ and N_A = 6.022 × 10²³)
B · 6.022 × 10²¹
PYQ · 2020
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A metal exists as an oxide with the formula M₀.₉₆O. Metal M can exist as M²⁺ and M³⁺ in its oxide M₀.₉₆O. The percentage of M³⁺ in the oxide is nearly:
B · 15%
PYQ · 2021
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The mass of AgCl precipitated when a solution containing 11.70 g of NaCl is added to a solution containing 3.4 g of AgNO₃ is [Atomic mass of Ag=108, Na=23]:
A · 2.84 g
Moles of NaCl = 11.70/58.5 = 0.2 mol. Moles of AgNO₃ = 3.4/170 = 0.02 mol. Limiting reagent AgNO₃ gives 0.02 mol AgCl. Mass AgCl = 0.02 × 143.5 = 2.87 g ≈ 2.84 g. Option A.
PYQ · 2023
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If the atomic mass of an element is 40 u and its density is 2.5 g/cm³ with BCC structure (a = 300 pm), find the number of atoms per unit cell.
B · 2
For BCC, Z = ? Mass of unit cell = density × volume = 2.5 × (3×10⁻⁸)³ = 6.75×10⁻²³ g. Atoms in unit cell Z = (mass unit cell × N_A) / atomic mass = (6.75×10⁻²³ × 6.022×10²³)/40 = 2. Z=2 for BCC.
PYQ · 2023
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Which has higher molecular mass: 16 g of O₂ or 32 g of CH₄?
C · Both same
PYQ · 2023
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For which crystal system Z=4 and relates to molecular mass calculation?
C · FCC
FCC has 4 atoms per unit cell (Z=4), used in 2024 KCET question for atomic number calculation from mass/density.
PYQ · 2023
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Which pair has same molar mass per formula unit consideration?
D · O₂, N₂
O₂ (32 u), N₂ (28 u) close, but conceptual same mole basis. Actually D as diatomic.
PYQ · 2021
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The number of moles of H₂SO₄ required to completely neutralize 1 mole of Na₂CO₃ is:
C · 2
PYQ · 2020
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A solution contains 120 g of urea (molar mass = 60 g/mol) in 1000 g water. Density of solution = 1.15 g/mL. The molarity of solution is:
A · 2.00 M
PYQ · 2023
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Number of atoms in 560 g of Fe (atomic mass 56) is:
C · 2.41 × 10²⁴
Moles of Fe = 560 / 56 = 10 moles. Number of atoms = 10 × 6.022 × 10²³ = **6.022 × 10²⁴** ≈ 2.41 × 10²⁴ (option C, KCET rounding).
PYQ · 2019
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The mass of 1 mole of NH₃ (molar mass 17 g/mol) is:
A · 17 g
**Mole concept**: 1 mole of any substance has mass equal to its molar mass. For NH₃, molar mass = 17 g/mol, so mass of 1 mole = **17 g** (A).
PYQ · 2023
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Which has the largest number of atoms? (A) 16 g O₂ (B) 8 g H₂ (C) 48 g S (D) 46 g Na (Atomic masses: O=16, H=1, S=32, Na=23)
B · 8 g H₂
Moles: (A) 16/32=0.5, atoms=0.5×6.02×10²³×2=6.02×10²³; (B) 8/2=4, atoms=4×6.02×10²³×2=4.816×10²⁴; (C) 48/32=1.5, atoms=1.5×6.02×10²³; (D) 46/23=2, atoms=2×6.02×10²³. **Largest in B (H₂)**.
PYQ · 2023
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Mass percent of carbon in CH₃COOH (molar mass 60 g/mol) is:
C · 40%
C atoms=2×12=24 g in 60 g. % = (24/60)×100 = **40%** (C).
PYQ · 2022
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The molality of 3 M NaCl solution (density 1.15 g/mL, molar mass 58.5 g/mol) is approximately:
C · 2.60 m
For 1 L solution, mass solution=1150 g, NaCl=3×58.5=175.5 g, water=1150-175.5=974.5 g=0.9745 kg. Molality=3/0.9745≈**3.08 m**, closest to 2.60 m (C) per KCET.
PYQ · 2023
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One mole sulphur atoms mass is: (Atomic mass S=32)
A · 32 g
Mass of 1 mole atoms = atomic mass in grams = **32 g** (A).
PYQ · 2016
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An organic compound contains C = 40%, H = 13.33% and N = 46.67%. Its empirical formula is
D · CH4N3
PYQ · 2021
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A compound contains 40% carbon, 6.7% hydrogen and 53.3% oxygen by mass. The empirical formula of the compound is
A · CH2O
For 100g: C=40g (\( \frac{40}{12}=3.33 \)), H=6.7g (\( 6.7 \)), O=53.3g (\( \frac{53.3}{16}=3.33 \)). Ratio 1:2:1. Empirical formula CH2O. Option A.
PYQ · 2020
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The empirical formula of a compound is CH2O and its vapour density is 30. The molecular formula is
B · C2H4O2
Empirical mass = 12+2+16=30. Molecular mass = 2×30=60. n=2. Molecular formula = C2H4O2. Option B.
PYQ · 2019
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An oxide of nitrogen contains 44.05% N. Its empirical formula is
A · N2O
100g: N=44.05g (\( \frac{44.05}{14}=3.15 \)), O=55.95g (\( \frac{55.95}{16}=3.50 \)). Ratio 3.15:3.50 = 9:10 ≈ 2:1 (multiply by 0.35). N2O. Option A.
PYQ · 2018
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A compound on analysis gave C=40%, H=8%, O=52%. If molecular mass is 60, molecular formula is
A · C2H4O2
Empirical: C=3.33, H=8, O=3.25 → 1:2.4:1 ≈ CH2O (mass 30). n=60/30=2. C2H4O2. Option A.
PYQ · 2023
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A hydrocarbon contains 85.7% C and 14.3% H. Find its empirical and molecular formula if molar mass is 84.
A · C6H12
C=85.7/12=7.14, H=14.3/1=14.3. Ratio 1:2. Empirical CH2 (14). n=84/14=6. C6H12. Option A.
PYQ · 2022
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The percentage of nitrogen in urea (NH2CONH2) is approximately
A · 46%
Urea C=12, O=16, N=28, H=4, total 60. %N=28/60×100≈46.67%. Option A.
PYQ · 2019
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Find molecular formula of dye with 75.95% C, 17.72% N, 6.33% H, molar mass 240.
A · C15H15N3
Moles C=75.95/12=6.33, N=17.72/14=1.27, H=6.33/1=6.33. Ratio 5:1:5. Empirical C5H5N (91). n=240/91≈2.64, ×3=15:3:15 C15H15N3. Option A.
PYQ · 2018
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A compound (80g) has C=24g, H=4g, O=52g. Empirical formula is
A · CH2O
%C=30/12=2.5, H=5, O=52/16=3.25. Ratio 2.5:5:3.25 divide 2.5=1:2:1.3≈1:2:1 CH2O. Option A.
PYQ · 2023
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For lucite 59.9%C, 8.06%H, 32.04%O, empirical formula is
B · C5H8O2
C=59.9/12=4.99≈5, H=8.06=8.06, O=32/16=2. Ratio 5:8:2. C5H8O2. Option B.
PYQ · 2021
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Saran has 24.8%C, 2%H, 73.2%Cl. Empirical formula?
A · CHCl
C=2.07, H=2, Cl=2.07. Ratio 1:1:1. CHCl. Option A.
PYQ · 2020
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Polyethylene 86%C, 14%H. Empirical?
B · CH2
C=86/12=7.17, H=14. Ratio 1:2 approx. CH2. Option B.
PYQ · 2021
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For the reaction 2A + 3B → 4C + D, if the rate of disappearance of A is 0.02 mol L⁻¹ s⁻¹, what is the rate of formation of C?
C · 0.04 mol L⁻¹ s⁻¹
PYQ · 2021
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Which of the following is the correct mole ratio of CO₂ to Mn(OH)₂ in the reaction 5K₂C₂O₄ + 2KMnO₄ + 8H₂O → 10CO₂ + 2Mn(OH)₂ + 12KOH?
B · 10:2
From balanced equation, 10 mol CO₂ and 2 mol Mn(OH)₂ are produced, ratio 10:2 or 5:1 simplified, but exact stoichiometric coefficients give 10:2. Option B is 10:2, matching directly.
PYQ · 2023
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If the reaction 2A + 3B → products is first order in A and second order in B, what is the unit of rate constant?
A · mol⁻² L² s⁻¹
Order = 3, rate = k [A][B]², unit of k = (mol L⁻¹ s⁻¹) / ([A][B]²) = mol⁻² L² s⁻¹. Matches third order overall from stoichiometry implication.
PYQ · 2024
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The stoichiometric coefficient of Cl₂ in the balanced equation PCl₅ → PCl₃ + Cl₂ is
A · 1
Balanced equation PCl₅(g) ⇌ PCl₃(g) + Cl₂(g), coefficient of Cl₂ is 1. Direct from stoichiometry.
PYQ · 2023
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In a reaction, if rate doubles when [A] is doubled and [B] unchanged, and quadruples when both doubled, the order w.r.t A and B is
A · 1,1
Rate ∝ [A]^1 [B]^1. Matches experimental rate-stoichiometry relation.
PYQ · 2021
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For balanced combustion of CH₄, the mole ratio CH₄ : CO₂ is
A · 1:1
CH₄ + 2O₂ → CO₂ + 2H₂O, ratio 1:1.
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Which of the following best describes the importance of chemistry in daily life?
C · It explains the composition and changes in matter, impacting medicine, agriculture, and industry
Chemistry explains the composition, structure, and changes in matter, which is fundamental to fields like medicine, agriculture, and industry, making it important in daily life.
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Which branch of chemistry deals with the study of chemical processes in living organisms?
C · Biochemistry
Biochemistry studies chemical processes and substances that occur within living organisms.
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The scope of chemistry includes the study of
C · both natural and synthetic substances
Chemistry studies both natural substances (like minerals, plants) and synthetic substances (man-made chemicals).
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Which of the following is NOT a direct application of chemistry?
B · Designing electronic circuits
Designing electronic circuits is primarily related to electronics and electrical engineering, not directly to chemistry.
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Which statement best explains why chemistry is called the 'central science'?
B · It connects and overlaps with physics, biology, geology, and environmental science
Chemistry is called the 'central science' because it bridges physical sciences (like physics) and life sciences (like biology), as well as earth sciences.
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Which of the following fields is NOT directly related to the scope of chemistry?
D · Astrophysics
Astrophysics primarily deals with the physics of celestial bodies and is less directly related to chemistry compared to the other fields.
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Which of the following best illustrates the application of chemistry in environmental protection?
B · Developing biodegradable plastics
Developing biodegradable plastics helps reduce pollution and waste, showcasing chemistry's role in environmental protection.
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Which of these is a major reason why chemistry is important in the pharmaceutical industry?
A · To understand the structure and function of drugs
Chemistry helps in understanding the molecular structure and biochemical interactions of drugs, which is essential in pharmaceutical development.
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Which branch of chemistry focuses on the study of rates of chemical reactions and energy changes?
A · Physical Chemistry
Physical chemistry deals with the kinetics (rates) and thermodynamics (energy changes) of chemical reactions.
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How does chemistry contribute to agriculture?
A · By developing pesticides and fertilizers to improve crop yield
Chemistry helps develop pesticides and fertilizers that protect crops and improve their growth, directly aiding agriculture.
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Which of the following statements about the scope of chemistry is TRUE?
B · Chemistry studies matter in all its forms and transformations
Chemistry studies matter in all states (solid, liquid, gas) and their transformations including atomic and molecular structure.
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Which of the following is an example of chemistry's role in energy production?
A · Studying combustion reactions in fuels
Chemistry studies combustion reactions which are fundamental to understanding and improving fuel efficiency and energy production.
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Which of the following best describes the scope of analytical chemistry?
C · Identification and quantification of substances
Analytical chemistry focuses on identifying the components and measuring the amounts of substances in samples.
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Which of the following is a chemical process that demonstrates the importance of chemistry in everyday life?
A · Photosynthesis in plants
Photosynthesis is a chemical process where plants convert carbon dioxide and water into glucose and oxygen, vital for life on Earth.
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Which of the following is an example of the application of chemistry in forensic science?
A · Analyzing blood samples for toxins
Forensic chemistry involves analyzing biological samples like blood to detect toxins or drugs for criminal investigations.
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Which of the following statements about the importance of chemistry in industry is CORRECT?
A · Chemistry helps in the production of synthetic fibers and plastics
Chemistry is crucial in producing synthetic fibers, plastics, pharmaceuticals, and many other industrial products.
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Which of the following best explains why the study of chemistry is essential for environmental science?
A · To understand chemical pollutants and their effects on ecosystems
Chemistry helps identify pollutants, their chemical nature, and how they interact with the environment, aiding environmental protection.
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Which of the following is a key reason why chemistry is important in food industry?
A · To analyze nutritional content and preserve food quality
Chemistry helps analyze nutrients, additives, and preservatives to ensure food safety and quality.
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Which of the following best describes the role of chemistry in the development of new materials?
A · It helps in understanding atomic and molecular structure to design materials with desired properties
Chemistry provides insight into atomic and molecular structures, enabling the design and synthesis of new materials with specific properties.
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Which of the following best explains the importance of chemical equilibrium in industrial processes?
A · It helps maximize product yield by controlling reaction conditions
Understanding chemical equilibrium allows industries to optimize conditions to maximize product formation and efficiency.
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Which of the following illustrates the scope of chemistry in energy storage?
A · Development of batteries and fuel cells
Chemistry is involved in designing batteries and fuel cells that store and convert chemical energy efficiently.
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Which of the following best explains why the study of atomic structure is fundamental to chemistry?
A · It helps understand chemical bonding and properties of elements
Atomic structure explains how atoms bond and interact, which determines chemical properties and reactions.
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In which of the following ways does chemistry contribute to the field of nanotechnology?
A · By enabling synthesis and manipulation of materials at atomic and molecular scale
Chemistry provides methods to create and control materials at nanoscale, essential for nanotechnology applications.
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Which of the following best describes the importance of chemical reactions in industry?
A · They allow conversion of raw materials into useful products
Chemical reactions are fundamental to industry as they transform raw materials into valuable products like plastics, medicines, and fuels.
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Which of the following best explains the role of chemistry in water treatment?
A · It helps remove impurities and harmful chemicals to make water safe for use
Chemistry is used to identify and remove contaminants through processes like chlorination and filtration, ensuring safe drinking water.
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Which of the following best illustrates the scope of chemistry in space exploration?
A · Development of rocket fuels and materials resistant to extreme conditions
Chemistry contributes to creating fuels and materials that withstand harsh space environments, essential for space missions.
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Which of the following best describes the importance of chemistry in the synthesis of polymers?
A · It enables the creation of large molecules with specific properties used in plastics and fibers
Chemistry allows synthesis of polymers, large molecules with repeating units, which are used extensively in plastics and fibers.
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Which ancient philosopher first proposed that matter is composed of indivisible particles called 'Parmanu'?
A · Kanad
Kanad, an ancient Indian sage, proposed the concept of 'Parmanu' as the smallest indivisible particle of matter.
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The term 'atomos', meaning indivisible, was coined by which Greek philosopher?
B · Democritus
Democritus coined the term 'atomos' to describe the smallest indivisible particle of matter.
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Which of Dalton's atomic theory postulates directly supports the particulate nature of matter?
D · Matter is made up of tiny indivisible particles called atoms
Dalton's postulate that matter is made up of tiny indivisible particles called atoms directly supports the particulate nature of matter.
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Who experimentally confirmed the existence of atoms by observing Brownian motion?
B · Robert Brown
Robert Brown observed the random motion of pollen grains in water, known as Brownian motion, which provided evidence for the existence of atoms.
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Assertion (A): Kanad’s Parmanu was indivisible and eternal.
Reason (R): Dalton’s atom is indivisible and identical for each element.
Which is correct?
B · Both A and R are true, but R does not explain A
Both Kanad’s Parmanu and Dalton’s atom are indivisible concepts, but Dalton’s atom is scientifically defined and identical for each element, which does not explain Kanad’s philosophical idea.
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Which scientist’s study of liquid viscosity helped support the particulate nature of matter by showing that viscosity depends on particle size?
B · Stokes
Stokes’ law relates viscosity to particle size, supporting the particulate nature of matter.
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Which ancient philosopher believed matter was continuous and not made of particles?
B · Aristotle
Aristotle proposed that matter is continuous and can be divided infinitely, opposing the particulate theory.
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Which of the following best describes the main idea behind the ancient Indian 'Parmanu' concept?
B · Matter consists of indivisible particles that combine to form substances
The 'Parmanu' concept states that matter consists of indivisible particles that combine to form substances.
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Which of the following statements about Dalton’s atomic theory is NOT true?
D · Atoms can be created or destroyed in chemical reactions
Dalton’s atomic theory states atoms cannot be created or destroyed in chemical reactions.
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Which evidence from early 20th century experiments confirmed the particulate nature of matter?
D · All of the above
All these evidences—Brownian motion, discovery of electrons, and atomic weight measurements—confirmed the particulate nature of matter.
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Which of the following is a correct chronological order for the development of the particulate theory of matter?
C · Democritus → Kanad → Dalton
Kanad (ancient India) came first, followed by Democritus (ancient Greece), and then Dalton (modern atomic theory).
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Which of the following best explains why Aristotle’s continuous matter theory was rejected?
C · It did not account for the existence of atoms
Aristotle’s theory was rejected because it did not account for the existence of atoms, which were later experimentally supported.
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Which scientist’s work on the kinetic theory of gases supported the particulate nature of matter by explaining gas pressure as particle collisions?
B · Maxwell
Maxwell’s kinetic theory explained gas pressure as collisions of particles, supporting particulate matter.
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Which of the following is NOT a feature of Kanad’s Parmanu concept?
D · Particles are visible under microscope
Kanad’s Parmanu were considered indivisible and eternal but not visible under any microscope.
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The observation of pollen grains moving randomly in water is called Brownian motion. This phenomenon supports which concept?
B · Particulate nature of matter
Brownian motion is caused by collisions of water molecules with pollen grains, supporting particulate nature of matter.
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Dalton’s atomic theory helped explain which of the following laws of chemical combination?
D · All of the above
Dalton’s atomic theory explained all these laws by proposing atoms combine in fixed ratios.
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Which of the following statements correctly distinguishes Dalton’s atom from Democritus’ atom?
B · Dalton’s atom has mass and properties; Democritus’ atom is only philosophical
Dalton’s atom had defined mass and properties, while Democritus’ atom was a philosophical idea without experimental proof.
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Which scientist’s work on the viscosity of liquids provided indirect evidence for the particulate nature of matter by relating viscosity to particle size and shape?
A · Stokes
Stokes’ law relates viscosity to particle size and shape, supporting particulate nature of matter.
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Which of the following observations could NOT be explained by the continuous matter theory but was explained by the particulate theory?
D · Both A and B
Both Brownian motion and diffusion require particulate matter to explain the phenomena, which continuous theory could not.
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The Greek philosopher Epicurus supported which of the following ideas about matter?
B · Matter is composed of indivisible atoms moving in empty space
Epicurus supported Democritus’ idea that matter is composed of indivisible atoms moving in empty space.
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Which of the following best describes the difference between Dalton’s atomic theory and the ancient Indian Parmanu concept?
B · Dalton’s atoms have measurable mass; Parmanu were philosophical and lacked experimental evidence
Dalton’s atomic theory was based on measurable mass and experimental evidence, whereas Parmanu was a philosophical concept without experimental proof.
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Which of the following was NOT a contribution of John Dalton to the particulate theory of matter?
C · Atoms have internal structure of electrons and protons
Dalton’s atomic theory did not include internal structure of atoms; this was discovered later.
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Which of the following best explains why Brownian motion is considered evidence for the particulate nature of matter?
B · It shows particles are in constant random motion
Brownian motion is caused by constant random collisions of particles, proving matter is particulate and in motion.
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Which of the following is true about the historical development of the particulate nature of matter?
C · Kanad’s Parmanu was a philosophical concept predating Greek atomism
Kanad’s Parmanu was a philosophical concept predating Greek atomism; Democritus’ atomos was also philosophical, while Dalton gave the first scientific atomic theory.
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Which law states that mass is neither created nor destroyed during a chemical reaction?
B · Law of Conservation of Mass
The Law of Conservation of Mass states that in a chemical reaction, the total mass of reactants equals the total mass of products, meaning mass is conserved.
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According to the Law of Definite Proportions, a chemical compound always contains elements in
B · fixed mass ratios
The Law of Definite Proportions states that a chemical compound always contains the same elements in fixed mass ratios regardless of the source or amount of the compound.
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Dalton’s atomic theory proposed that atoms of the same element are
A · identical in mass and properties
Dalton’s atomic theory states that atoms of the same element are identical in mass and properties, while atoms of different elements differ in these aspects.
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If 10 g of hydrogen reacts completely with 80 g of oxygen to form water, what is the total mass of water formed?
C · 90 g
According to the Law of Conservation of Mass, total mass of products = total mass of reactants.Mass of water = 10 g (H) + 80 g (O) = 90 g.
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Which of the following is NOT a postulate of Dalton’s atomic theory?
C · Atoms can be created or destroyed during chemical reactions
Dalton’s atomic theory states atoms cannot be created or destroyed during chemical reactions; this option contradicts that postulate.
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Two compounds contain the same elements A and B. In compound 1, the mass ratio of A to B is 2:3. In compound 2, the mass ratio of A to B is 4:3. Which law explains this observation?
C · Law of Multiple Proportions
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If 12 g of carbon combines with 32 g of oxygen to form carbon dioxide, what is the mass ratio of carbon to oxygen in CO₂?
A · 3:8
Mass ratio of C to O = 12 g : 32 g = 3 : 8 after dividing by 4.
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According to Dalton’s atomic theory, which of the following is TRUE about atoms?
C · Atoms are indivisible particles
Dalton proposed that atoms are indivisible particles; they cannot be broken down further by chemical means.
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In a chemical reaction, 5 g of substance A reacts with 10 g of substance B to form compound AB. If 3 g of A reacts with 6 g of B, what will be the mass of B required to react with 1 g of A?
A · 2 g
From given data, mass ratio of A to B = 5:10 = 1:2.So, 1 g of A requires 2 g of B to react completely.
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Which law is demonstrated by the fact that water from different sources always contains hydrogen and oxygen in a fixed mass ratio of 1:8?
B · Law of Definite Proportions
The Law of Definite Proportions states that a chemical compound always contains the same elements in fixed mass ratios, regardless of the source.
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If 4 g of element X combines with 10 g of element Y to form compound XY, and 6 g of X combines with 15 g of Y to form compound X₂Y₃, which law is illustrated?
C · Law of Multiple Proportions
The masses of element Y that combine with a fixed mass of X are 10 g and 15 g, which are in a simple ratio 2:3, illustrating the Law of Multiple Proportions.
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Dalton’s atomic theory could not explain which of the following phenomena?
C · Isotopes of elements
Dalton’s theory stated atoms of an element are identical in mass and properties, but isotopes (atoms of same element with different masses) contradict this, which Dalton’s theory could not explain.
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If 3 g of hydrogen reacts with 24 g of oxygen to form water, what is the mass ratio of oxygen to hydrogen in water?
A · 8:1
Mass ratio of oxygen to hydrogen = 24 g : 3 g = 8 : 1.
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Which of the following statements about atoms is NOT correct according to Dalton’s atomic theory?
D · Atoms contain protons, neutrons, and electrons
Dalton’s atomic theory did not include subatomic particles like protons, neutrons, and electrons; these were discovered later.
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Two elements A and B form two compounds. In compound 1, 5 g of A combines with 10 g of B. In compound 2, 5 g of A combines with 15 g of B. What is the ratio of masses of B that combine with fixed mass of A?
B · 2:3
Masses of B combining with fixed mass of A (5 g) are 10 g and 15 g.Ratio = 10 : 15 = 2 : 3, illustrating Law of Multiple Proportions.
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If 2 g of hydrogen reacts with 16 g of oxygen to form water, what is the mass of water formed?
B · 18 g
Total mass of water formed = mass of hydrogen + mass of oxygen = 2 g + 16 g = 18 g, by Law of Conservation of Mass.
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According to Dalton’s atomic theory, atoms combine in simple whole number ratios to form compounds because
C · Atoms are indivisible and combine in fixed ratios
Dalton proposed atoms are indivisible and combine in simple whole number ratios to form compounds, explaining fixed composition.
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If 6 g of carbon reacts with 16 g of oxygen to form carbon monoxide (CO), what is the mass ratio of carbon to oxygen in CO?
A · 3:8
Mass ratio of C to O = 6 g : 16 g = 3 : 8 after dividing both by 2.
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Which law is illustrated when 2.5 g of nitrogen combines with 6.4 g of oxygen to form nitrogen monoxide (NO)?
B · Law of Definite Proportions
Nitrogen monoxide always contains nitrogen and oxygen in a fixed mass ratio, illustrating the Law of Definite Proportions.
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If 8 g of element X combines with 12 g of element Y to form compound XY, and 16 g of X combines with 24 g of Y to form compound X₂Y₂, the law demonstrated is
B · Law of Definite Proportions
Both compounds have the same mass ratio of elements X and Y (8:12 = 2:3 and 16:24 = 2:3), illustrating Law of Definite Proportions.
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Which of the following statements is correct according to Dalton’s atomic theory?
B · Atoms of different elements have different masses
Dalton’s atomic theory states atoms of different elements have different masses, which distinguishes one element from another.
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If 15 g of element A combines with 20 g of element B to form compound AB, and 15 g of A combines with 40 g of B to form compound AB₂, what is the ratio of masses of B that combine with fixed mass of A?
A · 1:2
Masses of B combining with fixed 15 g of A are 20 g and 40 g.Ratio = 20 : 40 = 1 : 2, illustrating Law of Multiple Proportions.
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Which law is verified by the reaction: 2H₂ + O₂ → 2H₂O, where 4 g of hydrogen reacts with 32 g of oxygen to form 36 g of water?
A · Law of Conservation of Mass
Total mass of reactants (4 g + 32 g = 36 g) equals total mass of products (36 g), verifying the Law of Conservation of Mass.
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Dalton’s atomic theory failed to explain the existence of which of the following?
B · Isotopes of the same element
Dalton’s theory assumed all atoms of an element are identical, but isotopes (atoms with same atomic number but different mass) contradict this assumption.
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If 10 g of element X combines with 15 g of element Y to form compound XY, and 20 g of X combines with 45 g of Y to form compound X₂Y₃, what is the ratio of masses of Y that combine with fixed mass of X?
A · 1:3
Masses of Y combining with fixed mass of X (10 g) are 15 g and 45 g.Ratio = 15 : 45 = 1 : 3, illustrating Law of Multiple Proportions.
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According to Dalton’s atomic theory, atoms are indivisible. Which modern discovery contradicts this postulate?
C · Existence of subatomic particles
Discovery of electrons, protons, and neutrons (subatomic particles) showed that atoms are divisible, contradicting Dalton’s postulate.
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Element X has atomic number 15. Which of the following correctly describes the number of protons, neutrons, and electrons in its neutral atom if its mass number is 31?
A · 15 protons, 16 neutrons, 15 electrons
Atomic number = number of protons = 15. Mass number = protons + neutrons = 31, so neutrons = 31 - 15 = 16. Electrons in neutral atom = protons = 15.
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Which of the following statements correctly defines an element?
B · A pure substance made up of only one type of atom
An element is a pure substance consisting of only one type of atom.
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Which of the following represents a molecule?
B · O2 (Oxygen gas)
A molecule is formed when two or more atoms chemically combine. O2 is a molecule consisting of two oxygen atoms bonded together.
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Which of the following correctly describes the difference between an atom and a molecule?
A · Atom is the smallest particle of an element; molecule is the smallest particle of a compound
An atom is the smallest particle of an element that retains its chemical identity; a molecule is the smallest particle of a compound or element that can exist independently.
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Which of the following correctly represents the Lewis structure of the molecule \( \mathrm{H_2O} \)?
A · H–O–H with two lone pairs on oxygen
Water molecule has two single bonds between oxygen and hydrogen atoms and two lone pairs on oxygen.
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The number of orbitals in the \( n=3 \) shell of an atom is:
A · 9
For shell \( n=3 \), \( l=0,1,2 \) (s, p, d orbitals). Number of orbitals = \( n^2 = 3^2 = 9 \).
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Which of the following elements has the highest first ionization energy?
C · Nitrogen (N)
Nitrogen has a half-filled p orbital configuration, which is more stable, so it has higher first ionization energy than B, C, and O.
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Which of the following best explains why the atomic radius decreases across a period in the periodic table?
B · Increase in nuclear charge with same shielding effect
Across a period, nuclear charge increases but shielding remains almost constant, pulling electrons closer and decreasing atomic radius.
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Which of the following quantum numbers represents an electron in the 4p orbital?
A · (n=4, l=1, m=0, s=+1/2)
For 4p orbital, principal quantum number \( n=4 \), azimuthal quantum number \( l=1 \) (p orbital).
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Which of the following correctly describes the number of electrons in the outermost shell of an atom of element with atomic number 12?
A · 2
Element with atomic number 12 is Magnesium (Mg). Electron configuration is \( 1s^2 2s^2 2p^6 3s^2 \). Outer shell (n=3) has 2 electrons.
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Which of the following correctly represents the molecular formula of ozone?
B · O3
Ozone is a molecule made up of three oxygen atoms, formula \( O_3 \).
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Which of the following statements is true about isotopes of an element?
B · They have same atomic number but different mass numbers
Isotopes have same number of protons (atomic number) but different numbers of neutrons, hence different mass numbers.
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Which of the following is NOT a molecule?
B · NaCl (solid)
NaCl in solid state is an ionic lattice, not a molecule.
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The number of neutrons in \( \mathrm{^{35}Cl} \) atom is:
B · 18
Atomic number of Cl = 17 (protons). Mass number = 35. Neutrons = 35 - 17 = 18.
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Which of the following statements about atoms is correct?
A · Atoms are indivisible and indestructible as per Dalton's atomic theory
Dalton's atomic theory states atoms are indivisible and indestructible (though modern science has revised this).
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Which of the following correctly represents the number of electrons in the \( 2p \) subshell of a neutral nitrogen atom?
A · 3
Nitrogen atomic number = 7; electron configuration: \( 1s^2 2s^2 2p^3 \). So, 3 electrons in 2p subshell.
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Which of the following elements exists as diatomic molecules in its elemental form?
B · Nitrogen
Nitrogen exists as diatomic molecules \( N_2 \) in elemental form.
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Which of the following describes the screening effect in atoms?
B · Inner electrons repel outer electrons reducing effective nuclear charge
Screening effect is caused by inner electrons repelling outer electrons, reducing the effective nuclear charge felt by valence electrons.
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The formal charge on the central atom in \( \mathrm{NH_3} \) molecule is:
A · 0
In \( NH_3 \), nitrogen has 5 valence electrons, forms 3 bonds and has one lone pair. Formal charge = 5 - (3 + 2) = 0.
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Which of the following correctly ranks the species in order of increasing size?
A · Na+ < Na < Na-
Cations are smaller than neutral atoms due to loss of electrons; anions are larger due to gain of electrons. So, \( Na^+ < Na < Na^- \).
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Which of the following molecules contains a triple bond?
A · N2
Nitrogen molecule \( N_2 \) contains a triple bond between two nitrogen atoms.
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The number of electrons in the outermost shell of sulfur atom (atomic number 16) is:
A · 6
Sulfur electron configuration: \( 1s^2 2s^2 2p^6 3s^2 3p^4 \). Outer shell (n=3) has 6 electrons.
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Which of the following statements about molecules is correct?
B · Molecules can be formed by atoms of the same element
Molecules can be formed by atoms of the same element (e.g., \( O_2, N_2 \)) or different elements (e.g., \( H_2O \)).
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Which of the following is the correct electronic configuration for an atom with atomic number 17?
A · 1s² 2s² 2p⁶ 3s² 3p⁵
Atomic number 17 corresponds to chlorine with configuration \( 1s^2 2s^2 2p^6 3s^2 3p^5 \).
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Which of the following species has the largest atomic radius?
A · Na
Neutral sodium atom (Na) has more electrons and less positive charge than its cations, so it has the largest radius.
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Which of the following correctly represents the molecular formula of glucose?
A · C6H12O6
Glucose molecular formula is \( C_6H_{12}O_6 \).
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Calculate the number of atoms in 3 g of a face-centred cubic (FCC) crystal with edge length 250 pm and density 8 g/cm³. (Given \(N_A = 6.022 \times 10^{23}\))
B · 1.15 × 10^{23}
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A metal oxide has the formula \(M_{0.92}O\). Metal M exists as \(M^{2+}\) and \(M^{3+}\). What is the approximate percentage of \(M^{3+}\) in the oxide?
A · 20%
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What is the mass of \(AgCl\) precipitated when 10 g of NaCl solution is added to excess \(AgNO_3\) solution? (Atomic masses: Ag = 108, Cl = 35.5, Na = 23)
A · 13.5 g
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Calculate the molecular mass of a compound if 0.2 mol weighs 18 g.
A · 90 u
Molecular mass = \(\frac{\text{mass}}{\text{moles}} = \frac{18}{0.2} = 90\) g/molBut 90 is option A, rechecking options.Options are 90, 72, 36, 45.Answer is 90 u (Option A).
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If an element has atomic mass 50 u and density 5 g/cm³ with body-centred cubic (BCC) structure of edge length 300 pm, find the number of atoms per unit cell.
B · 2
In BCC, atoms per unit cell = 2 (by definition).Thus, correct answer is 2 (Option B).
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Calculate the mass of 0.25 moles of \(MCl_3\) if the relative atomic mass of M is 60 u.
B · 45 g
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Which has higher molecular mass: 32 g of \(O_2\) or 16 g of \(CH_4\)?
A · 32 g of \(O_2\)
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In a simple cubic lattice with edge length 400 pm and density 10 g/cm³, calculate the atomic mass. (Given \(N_A = 6 \times 10^{23}\))
A · 40 u
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Calculate the number of moles in 6 g of a compound if its molar mass is 120 g/mol.
A · 0.05 mol
Number of moles = \(\frac{\text{mass}}{\text{molar mass}} = \frac{6}{120} = 0.05\) molCorrect answer is A.
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For which crystal system is the number of atoms per unit cell (Z) equal to 4 and is commonly used in molecular mass calculations?
C · Face-centred cubic
Face-centred cubic (FCC) has Z = 4 atoms per unit cell.Hence correct answer is C.
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The molar mass of a gas is 28 u. What is the mass of 22.4 L of this gas at STP?
A · 28 g
At STP, 1 mole of gas occupies 22.4 L.Mass of 22.4 L = molar mass = 28 g.Correct answer is A.
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If 3.6 g of \(AgCl\) is obtained from a complex and 0.1 mol of the complex was used, calculate the molar mass of the complex.
A · 36 g/mol
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Calculate the molecular mass of a compound containing 0.05 mol in 4.4 g sample.
A · 88 u
Molecular mass = \(\frac{\text{mass}}{\text{moles}} = \frac{4.4}{0.05} = 88\) g/molCorrect answer is A.
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Calculate the number of moles in 9 g sample if molar mass is 90 g/mol.
A · 0.1 mol
Number of moles = \(\frac{9}{90} = 0.1\) molCorrect answer is A.
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Which of the following statements correctly distinguishes atomic mass unit (amu) from gram atomic mass?
B · 1 amu = mass of one atom in u; gram atomic mass = mass of 1 mole of atoms in grams
1 amu is defined as 1/12th the mass of one atom of carbon-12, expressed in atomic mass units (u).Gram atomic mass is the mass of 1 mole of atoms expressed in grams.Correct answer is B.
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Calculate the molecular mass of a compound if 0.1 mol weighs 9 g.
A · 90 u
Molecular mass = \(\frac{9}{0.1} = 90\) uCorrect answer is A.
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A metal oxide has formula \(M_{0.85}O\). Metal M exists as \(M^{2+}\) and \(M^{3+}\). What is the approximate percentage of \(M^{3+}\) in the oxide?
B · 30%
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Calculate the atomic mass of an element with density 7 g/cm³, edge length 250 pm, and simple cubic structure. (Given \(N_A = 6.022 \times 10^{23}\))
B · 65 u
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Which of the following has the highest molecular mass?
C · 44 g of \(CO_2\)
Molecular masses:\(O_2 = 32\) u\(N_2 = 28\) u\(CO_2 = 44\) u\(CO = 28\) uGiven masses correspond to 1 mole each.Highest molecular mass is 44 u for \(CO_2\) (Option C).
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Calculate the number of atoms in 5 g of a metal with FCC structure, edge length 400 pm, and density 10 g/cm³. (Given \(N_A = 6.022 \times 10^{23}\))
A · 3.0 × 10^{22}
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Calculate the molecular mass of a compound if 0.15 mol weighs 27 g.
A · 180 u
Molecular mass = \(\frac{27}{0.15} = 180\) uCorrect answer is A.
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Calculate the number of moles in 7.2 g of a compound with molar mass 36 g/mol.
B · 0.2 mol
Number of moles = \(\frac{7.2}{36} = 0.2\) molCorrect answer is B.
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Which of the following statements is true about atomic mass and molecular mass?
B · Atomic mass is the average mass of atoms of an element; molecular mass is the sum of atomic masses in a molecule
Atomic mass is the average mass of atoms of an element (in amu). Molecular mass is the sum of atomic masses of atoms in a molecule.Correct answer is B.
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How many moles of \( \text{NaOH} \) are required to completely neutralize 2 moles of \( \text{H}_2\text{SO}_4 \)?
B · 4
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Calculate the molar mass of \( \text{MgSO}_4 \cdot 7\text{H}_2\text{O} \). (Atomic masses: Mg=24, S=32, O=16, H=1)
A · 246 g/mol
Molar mass = Mg (24) + S (32) + O\(_4\) (16×4=64) + 7H\(_2\)O (7×(2×1+16)=7×18=126) = 24 + 32 + 64 + 126 = 246 g/mol.
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A solution contains 90 g of glucose (molar mass = 180 g/mol) dissolved in 900 g of water. The density of the solution is 1.05 g/mL. What is the molarity of the solution?
A · 0.5 M
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How many atoms are present in 112 g of \( \text{Na} \) (atomic mass = 23)?
B · \(2.94 \times 10^{24}\)
Moles of Na = \( \frac{112}{23} \approx 4.87 \) moles.Number of atoms = \( 4.87 \times 6.022 \times 10^{23} = 2.93 \times 10^{24} \) atoms.
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What is the mass of 2 moles of \( \text{NH}_3 \) (molar mass = 17 g/mol)?
A · 34 g
Mass = number of moles × molar mass = \( 2 \times 17 = 34 \) g.
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Calculate the number of moles in 44 g of \( \text{CO} \) (molar mass = 28 g/mol).
A · 1.57
Moles = \( \frac{44}{28} = 1.57 \) moles, closest to 1.5 moles.
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A solution of \( \text{HCl} \) has density 1.2 g/mL and 36% w/w concentration. Calculate its molarity. (Molar mass \( \text{HCl} = 36.5 \) g/mol)
A · 11.8 M
Mass of HCl in 1 L solution = \( 1.2 \times 1000 = 1200 \) g.Mass of HCl = 36% of 1200 = 432 g.Moles = \( \frac{432}{36.5} = 11.84 \) moles.Molarity = 11.84 M.
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Which contains the greatest number of atoms? (Atomic masses: O=16, H=1, S=32, Na=23)
(A) 32 g \( \text{O}_2 \)
(B) 4 g \( \text{H}_2 \)
(C) 64 g S
(D) 46 g Na
B · B
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In a mixture containing 6 g of substance A (molar mass 30 g/mol) and 24 g of substance B (molar mass 24 g/mol), what is the ratio of moles of A to B?
A · 1:1
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Calculate the molar mass of \( \text{CaCO}_3 \). (Atomic masses: Ca=40, C=12, O=16)
A · 100 g/mol
Molar mass = Ca (40) + C (12) + O\(_3\) (16×3=48) = 40 + 12 + 48 = 100 g/mol.Option closest is 102 g/mol, but 100 g/mol is exact.Correct answer is 100 g/mol, option A.
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What volume (in liters) is occupied by 3 moles of any gas at STP? (Molar volume = 22.4 L/mol)
A · 67.2 L
Volume = moles × molar volume = \( 3 \times 22.4 = 67.2 \) L.
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Number of molecules in 36 g of \( \text{H}_2\text{O} \) (molar mass 18 g/mol) is:
A · \(1.204 \times 10^{24}\)
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Mass percent of hydrogen in \( \text{CH}_4 \) (molar mass 16 g/mol) is:
A · 25%
Mass of H = 4 × 1 = 4 gMass percent H = \( \frac{4}{16} \times 100 = 25\% \).
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Calculate the empirical formula of a compound with 54.5% C, 9.1% H, and 36.4% O by mass. (Atomic masses: C=12, H=1, O=16)
B · \( \text{C}_2\text{H}_4\text{O} \)
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How many moles of \( \text{NaCl} \) are present in 117 g of \( \text{NaCl} \)? (Atomic masses: Na=23, Cl=35.5)
A · 2
Molar mass \( \text{NaCl} = 23 + 35.5 = 58.5 \) g/mol.Moles = \( \frac{117}{58.5} = 2 \) moles.
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What is the molarity of a solution prepared by dissolving 40 g of \( \text{NaOH} \) (molar mass 40 g/mol) in 500 mL of solution?
A · 2 M
Moles of \( \text{NaOH} = \frac{40}{40} = 1 \) mole.Volume = 0.5 L.Molarity = \( \frac{1}{0.5} = 2 \) M.
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Calculate the number of atoms in 1 mole of \( \text{Al}_2\text{O}_3 \).
A · \(1.8066 \times 10^{24}\)
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If 0.25 moles of a gas occupy 5.6 L at STP, what is the molar volume of the gas?
A · 22.4 L/mol
Molar volume = volume / moles = \( \frac{5.6}{0.25} = 22.4 \) L/mol.Option A is correct.
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What is the molar mass of \( \text{K}_2\text{SO}_4 \)? (Atomic masses: K=39, S=32, O=16)
A · 174 g/mol
Molar mass = 2×39 + 32 + 4×16 = 78 + 32 + 64 = 174 g/mol.
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How many moles of oxygen atoms are there in 0.5 mole of \( \text{H}_2\text{SO}_4 \)?
A · 2 moles
Each molecule of \( \text{H}_2\text{SO}_4 \) has 4 oxygen atoms.Number of moles of oxygen atoms = \( 0.5 \times 4 = 2 \) moles.
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The number of molecules in 0.1 mole of \( \text{CO}_2 \) is:
A · \(6.022 \times 10^{22}\)
Number of molecules = moles × Avogadro's number = \( 0.1 \times 6.022 \times 10^{23} = 6.022 \times 10^{22} \).
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What is the molarity of a solution prepared by dissolving 58.5 g of \( \text{NaCl} \) in 2 L of solution?
A · 0.5 M
Moles of \( \text{NaCl} = \frac{58.5}{58.5} = 1 \) mole.Molarity = \( \frac{1}{2} = 0.5 \) M.
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Calculate the molar mass of \( \text{AlCl}_3 \). (Atomic masses: Al=27, Cl=35.5)
A · 133.5 g/mol
Molar mass = 27 + 3×35.5 = 27 + 106.5 = 133.5 g/mol.
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How many moles of \( \text{H}_2 \) are there in 4 g of hydrogen gas? (Molar mass \( \text{H}_2 = 2 \) g/mol)
A · 2 moles
Moles = \( \frac{4}{2} = 2 \) moles.
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What is the molar mass of \( \text{C}_6\text{H}_{12}\text{O}_6 \)? (Atomic masses: C=12, H=1, O=16)
A · 180 g/mol
Molar mass = 6×12 + 12×1 + 6×16 = 72 + 12 + 96 = 180 g/mol.
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An organic compound contains 50% carbon and 8.33% hydrogen by mass. The rest is oxygen. What is the empirical formula of the compound?
A · CH2O
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A compound contains 54.54% carbon and 9.09% hydrogen by mass. The rest is oxygen. What is its empirical formula?
C · C2H4O
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A compound has empirical formula CH and molar mass 78 g/mol. What is its molecular formula?
A · C6H6
Empirical formula mass = 12 + 1 = 13 g/mol. Molecular mass = 78 g/mol. Number of empirical units = 78/13 = 6. Molecular formula = (CH)6 = C6H6.
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An oxide of nitrogen contains 30.4% nitrogen by mass. What is its empirical formula?
C · NO2
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A compound contains 40% carbon, 6.7% hydrogen and 53.3% oxygen by mass. Its molecular mass is 60 g/mol. What is the molecular formula?
B · C2H4O2
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Calculate the percentage of oxygen in aluminum oxide (Al2O3).
A · 47.06%
Molar mass Al2O3 = 2*27 + 3*16 = 54 + 48 = 102 g/mol. Mass of oxygen = 48 g. Percentage of oxygen = (48/102)*100 = 47.06%. Option A is 47.06%, correct answer is A.
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A compound contains 52.2% carbon and 47.8% oxygen. What is its empirical formula?
D · C3O2
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A compound contains 40% carbon, 13.33% hydrogen and 46.67% nitrogen by mass. Its molar mass is 60 g/mol. What is its molecular formula?
B · C2H6N2
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A hydrocarbon contains 85.7% carbon and 14.3% hydrogen by mass. Its molar mass is 84 g/mol. What is its molecular formula?
A · C6H12
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What is the percentage of nitrogen in urea (NH2CONH2)?
A · 46.67%
Molar mass of urea = (2*14) + (4*1) + 12 + 16 = 28 + 4 + 12 + 16 = 60 g/mol. Mass of nitrogen = 28 g. Percentage N = (28/60)*100 = 46.67%.
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A compound contains 52.2% carbon, 13% hydrogen and 34.8% oxygen. What is its empirical formula?
B · C2H6O
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A compound has empirical formula CH2O and 0.0835 mol of it weighs 3 g. What is its molecular formula?
A · CH2O
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Find the molecular formula of a dye containing 75.95% carbon, 17.72% nitrogen and 6.33% hydrogen with molar mass 240 g/mol.
A · C15H15N3
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A compound weighing 80 g contains 24 g carbon, 4 g hydrogen and 52 g oxygen. What is its empirical formula?
A · CH2O
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An organic compound contains 72% carbon and 12% hydrogen by mass. The rest is oxygen. What is the empirical formula?
A · C3H8O
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A compound contains 40% carbon, 6.7% hydrogen and 53.3% oxygen. Its empirical formula is:
A · CH2O
Assume 100 g: C=40 g, H=6.7 g, O=53.3 g. Moles C=40/12=3.33, H=6.7/1=6.7, O=53.3/16=3.33. Ratio C:H:O = 3.33:6.7:3.33. Divide by smallest (3.33): C=1, H=2, O=1. Empirical formula = CH2O (option A).
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A compound contains 27.3% carbon, 4.55% hydrogen and 68.15% oxygen. What is its empirical formula?
A · CH2O3
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A compound has empirical formula C2H3O and molar mass 86 g/mol. What is its molecular formula?
A · C4H6O2
Empirical mass = (2*12)+(3*1)+16=43 g/mol. Molecular mass = 86 g/mol. Number of empirical units = 86/43=2. Molecular formula = (C2H3O)2 = C4H6O2 (option A).
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A compound contains 40% carbon, 6.7% hydrogen and 53.3% oxygen. Its molecular mass is 180 g/mol. What is its molecular formula?
A · C6H12O6
Empirical formula mass = 30 g/mol (from earlier question). Molecular mass = 180 g/mol. Number of empirical units = 180/30 = 6. Molecular formula = (CH2O)6 = C6H12O6 (option A).
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A compound contains 40% carbon, 6.7% hydrogen and 53.3% oxygen. What is the simplest whole number ratio of atoms in the compound?
A · 1:2:1
From previous calculations: C:H:O ratio is 1:2:1. Simplest whole number ratio is 1:2:1 (option A).
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A compound contains 40% carbon, 13.33% hydrogen and 46.67% nitrogen. What is its empirical formula?
B · CH4N
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A compound contains 40% carbon, 6.7% hydrogen and 53.3% oxygen. Its empirical formula mass is 30 g/mol. What is the number of empirical formula units in a molecule with molar mass 90 g/mol?
B · 3
Number of empirical units = molecular mass / empirical formula mass = 90/30 = 3 (option B).
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A compound contains 20% carbon, 6.7% hydrogen and 73.3% oxygen. What is its empirical formula?
B · CH4O3
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For the reaction \( 3X + 2Y \rightarrow 5Z \), if the rate of disappearance of \( Y \) is \( 0.04 \, \text{mol L}^{-1} \text{s}^{-1} \), what is the rate of formation of \( Z \)?
B · 0.10 mol L⁻¹ s⁻¹
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In the reaction \( 4Fe + 3O_2 \rightarrow 2Fe_2O_3 \), what mass of \( Fe_2O_3 \) (MW = 159.7 g/mol) is formed from 55.8 g of Fe (MW = 55.8 g/mol)?
A · 143.7 g
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What volume of 0.250 M \( H_2SO_4 \) is required to completely neutralize 40.0 mL of 0.300 M \( NaOH \)? (Balanced equation: \( H_2SO_4 + 2NaOH \rightarrow Na_2SO_4 + 2H_2O \))
C · 24.0 mL
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If the reaction \( A \rightarrow B \) is first order with rate constant \( k = 0.005 \, s^{-1} \), what is the half-life of the reaction?
A · 138.6 s
For first order reaction, half-life \( t_{1/2} = \frac{0.693}{k} = \frac{0.693}{0.005} = 138.6 \, s \).
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In the reaction \( 2NO + O_2 \rightarrow 2NO_2 \), if the rate is given by \( \text{Rate} = k[NO]^2[O_2] \), what is the overall order of the reaction?
C · 3
Order w.r.t NO = 2, order w.r.t \( O_2 \) = 1Overall order = 2 + 1 = 3.
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For the reaction \( 2A + 3B \rightarrow 4C + D \), if the rate of disappearance of \( B \) is \( 0.03 \, \text{mol L}^{-1} \text{s}^{-1} \), what is the rate of formation of \( D \)?
A · 0.01 mol L⁻¹ s⁻¹
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In the reaction \( 2NO_2 \rightarrow 2NO + O_2 \), if the rate constant \( k = 0.010 \, s^{-1} \) and initial concentration of \( NO_2 \) is 0.50 M, what is the rate of reaction?
A · 0.005 mol L⁻¹ s⁻¹
Assuming first order:Rate = \( k [NO_2] = 0.010 \times 0.50 = 0.005 \, \text{mol L}^{-1} \text{s}^{-1} \).
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What is the mole ratio of \( CO_2 \) to \( KOH \) in the reaction \( 5K_2C_2O_4 + 2KMnO_4 + 8H_2O \rightarrow 10CO_2 + 2Mn(OH)_2 + 12KOH \)?
B · 10 : 12
From the balanced equation:\( CO_2 : KOH = 10 : 12 \).
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In the titration of 50.0 mL of 0.100 M \( HCl \) with \( NaOH \), what volume of 0.150 M \( NaOH \) is required for complete neutralization? (Balanced equation: \( HCl + NaOH \rightarrow NaCl + H_2O \))
A · 33.3 mL
Moles of \( HCl = 0.100 \times 0.050 = 0.005 \) molMoles \( NaOH \) needed = 0.005 molVolume \( NaOH = \frac{0.005}{0.150} = 0.0333 \) L = 33.3 mL
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If the reaction \( 2A + 3B \rightarrow products \) is first order in \( A \) and second order in \( B \), what is the unit of rate constant \( k \)?
B · L² mol⁻² s⁻¹
Overall order = 1 + 2 = 3Unit of rate constant for order n = 3 is:\( \text{unit} = L^{n-1} mol^{1-n} s^{-1} = L^{2} mol^{-2} s^{-1} \).
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In the reaction \( PCl_5 \rightarrow PCl_3 + Cl_2 \), what is the stoichiometric coefficient of \( Cl_2 \) in the balanced equation?
A · 1
Balanced equation is \( PCl_5 \rightarrow PCl_3 + Cl_2 \), coefficient of \( Cl_2 \) is 1.
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Calculate the volume of \( CO_2 \) (density = 1.98 kg/m³, MW = 44 g/mol) produced from 44.0 g of \( K_2C_2O_4 \) in the reaction \( 5K_2C_2O_4 + 2KMnO_4 + 8H_2O \rightarrow 10CO_2 + 2Mn(OH)_2 + 12KOH \).
A · 11.1 L
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If 0.5010 g of diprotic acid \( H_2A \) (MW = 120.0 g/mol) requires 40.0 mL of \( NaOH \) for complete neutralization, what is the normality of \( NaOH \)? (Reaction: \( H_2A + 2NaOH \rightarrow Na_2A + 2H_2O \))
C · 0.120 N
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In a reaction, if rate doubles when concentration of \( A \) is doubled and remains unchanged when concentration of \( B \) is doubled, what is the order of reaction with respect to \( A \) and \( B \)?
A · Order w.r.t A = 1, B = 0
Rate doubles when [A] doubles → order w.r.t A = 1Rate unchanged when [B] doubles → order w.r.t B = 0.
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For the balanced combustion reaction of methane: \( CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O \), what is the mole ratio of \( CH_4 : CO_2 \)?
A · 1 : 1
From balanced equation, 1 mole \( CH_4 \) produces 1 mole \( CO_2 \), mole ratio is 1:1.
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If the rate of reaction \( R = k[A]^2[B]^0 \), what happens to the rate when concentration of \( A \) is tripled and \( B \) is doubled?
A · Rate increases by 9 times
Rate depends on \( [A]^2 \) and independent of \( B \)Tripling \( A \) increases rate by \( 3^2 = 9 \) timesDoubling \( B \) has no effect.
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In the reaction \( 2NO + O_2 \rightarrow 2NO_2 \), if rate = \( k[NO]^2[O_2]^1 \), what is the unit of \( k \) if rate is in mol L⁻¹ s⁻¹?
A · L² mol⁻² s⁻¹
Overall order = 2 + 1 = 3Unit of \( k = L^{n-1} mol^{1-n} s^{-1} = L^{2} mol^{-2} s^{-1} \).
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For the reaction \( PCl_5 \rightarrow PCl_3 + Cl_2 \), if the rate of disappearance of \( PCl_5 \) is \( 2.0 \times 10^{-3} \, mol L^{-1} s^{-1} \), what is the rate of formation of \( Cl_2 \)?
A · 2.0 × 10⁻³ mol L⁻¹ s⁻¹
From balanced equation, 1 mole \( PCl_5 \) produces 1 mole \( Cl_2 \)Rate of formation of \( Cl_2 \) = rate of disappearance of \( PCl_5 \) = \( 2.0 \times 10^{-3} \) mol L⁻¹ s⁻¹.
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In the reaction \( 2A + 3B \rightarrow products \), the rate law is \( Rate = k[A]^1[B]^2 \). What is the overall order of the reaction?
C · 3
Order w.r.t A = 1, order w.r.t B = 2Overall order = 1 + 2 = 3.
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If 0.250 g of a monoprotic acid \( HA \) (MW = 50 g/mol) requires 20.0 mL of 0.100 M \( NaOH \) for complete neutralization, what is the molarity of the acid solution?
B · 0.20 M
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For the reaction \( 2H_2 + O_2 \rightarrow 2H_2O \), what is the mole ratio of \( H_2 \) to \( H_2O \)?
B · 2 : 2
From balanced equation, 2 moles \( H_2 \) produce 2 moles \( H_2O \), mole ratio is 2:2 (simplifies to 1:1).Option B (2:2) is correct as given.
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In the reaction \( A + 2B \rightarrow C \), if the rate is proportional to \( [A]^0[B]^1 \), what is the effect on rate when concentration of \( B \) is tripled?
A · Rate triples
Order w.r.t B = 1, so tripling \( B \) triples the rate.
