1. Which of the following SI units is used to express the amount of a substance?
A. Mole (mol)
B. Kilogram (kg)
C. Gram (g)
D. Ampere (A)
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Answer: A. Mole (mol)
Explanation: Mole is the standard SI base unit used to measure the amount of substance in chemistry.
2. The value of Avogadro's constant is:
A. 6.022 × 10²³ mol⁻¹
B. 6.022 × 10²² mol⁻¹
C. 6.022 × 10²⁴ mol⁻¹
D. 1.660 × 10⁻²⁴ mol⁻¹
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Answer: A. 6.022 × 10²³ mol⁻¹
Explanation: Avogadro's constant represents the exact number of elementary entities in one mole of a substance.
3. What is the mass of 1 mole of carbon-12 atom?
A. 12 g
B. 12 amu
C. 1 g
D. 6 g
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Answer: A. 12 g
Explanation: One mole of carbon-12 atoms weighs exactly 12 grams (its molar mass).
4. Which of the following laws states that a chemical compound always contains exactly the same proportion of elements by mass?
A. Law of Definite Proportions
B. Law of Conservation of Mass
C. Law of Multiple Proportions
D. Gay Lussac's Law
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Answer: A. Law of Definite Proportions
Explanation: Proposed by Joseph Proust, this law states that a given compound always contains elements in fixed mass ratios.
5. The empirical formula of glucose (C₆H₁₂O₆) is:
A. CH₂O
B. CHO
C. C₂H₄O₂
D. CH₃O
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Answer: A. CH₂O
Explanation: Dividing the subscripts (6:12:6) by their greatest common divisor (6) gives the simplest whole-number ratio: CH₂O.
6. The concentration term that depends on temperature is:
A. Molarity
B. Molality
C. Mole fraction
D. Mass percentage
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Answer: A. Molarity
Explanation: Molarity depends on the volume of the solution, which changes with temperature variations.
7. How many significant figures are there in 0.0025?
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Answer: A. 2
Explanation: Leading zeros before non-zero digits are not significant, so only '2' and '5' are significant.
8. What is the molarity of a solution containing 4 grams of NaOH in 250 mL of solution?
A. 0.4 M
B. 0.1 M
C. 0.2 M
D. 1.0 M
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Answer: A. 0.4 M
Explanation: Moles of NaOH = 4 / 40 = 0.1 mol. Volume = 0.25 L. Molarity = 0.1 / 0.25 = 0.4 M.
9. The mass of one molecule of water (H₂O) is approximately:
A. 2.99 × 10⁻²³ g
B. 18 g
C. 6.022 × 10⁻²³ g
D. 3.0 × 10⁻²² g
Show Answer
Answer: A. 2.99 × 10⁻²³ g
Explanation: Molar mass of water = 18 g/mol. Mass of 1 molecule = 18 / (6.022 × 10²³) ≈ 2.99 × 10⁻²³ g.
10. The reactant that gets completely consumed in a chemical reaction is known as the:
A. Limiting reagent
B. Excess reagent
C. Solute
D. Catalyst
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Answer: A. Limiting reagent
Explanation: The limiting reagent limits the extent of a reaction because it is consumed first.
11. What is the volume occupied by 1 mole of an ideal gas at Standard Temperature and Pressure (STP)?
A. 22.4 L
B. 11.2 L
C. 44.8 L
D. 24.5 L
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Answer: A. 22.4 L
Explanation: One mole of any ideal gas occupies 22.4 liters at STP (0°C and 1 atm pressure).
12. Who proposed the Law of Multiple Proportions?
A. John Dalton
B. Antoine Lavoisier
C. Joseph Proust
D. Joseph Louis Gay-Lussac
Show Answer
Answer: A. John Dalton
Explanation: John Dalton formulated the Law of Multiple Proportions in 1803.
13. What is the mass percentage of Hydrogen in H₂O? (Atomic mass: H = 1, O = 16)
A. 11.11%
B. 88.89%
C. 5.55%
D. 20.00%
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Answer: A. 11.11%
Explanation: Mass % of H = (2 / 18) × 100 = 11.11%.
14. Which of the following pairs of compounds illustrates the Law of Multiple Proportions?
A. CO and CO₂
B. NaCl and NaBr
C. H₂O and D₂O
D. MgO and MgCl₂
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Answer: A. CO and CO₂
Explanation: CO and CO₂ are formed by the same elements (C and O) combining in different simple whole-number ratios.
15. What is the molality of a solution containing 1 mole of solute in 1000 grams of solvent?
A. 1 m
B. 1 M
C. 0.5 m
D. 2 m
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Answer: A. 1 m
Explanation: Molality is defined as the number of moles of solute per kilogram (1000 g) of solvent.
16. The atomic mass unit (amu) is defined as:
A. 1/12th the mass of one carbon-12 atom
B. Mass of one hydrogen atom
C. 1/16th the mass of one oxygen-16 atom
D. Mass of one neutron
Show Answer
Answer: A. 1/12th the mass of one carbon-12 atom
Explanation: 1 amu is defined as exactly 1/12th of the mass of a single carbon-12 isotope atom.
17. Which of the following contains the maximum number of atoms?
A. 1 g of Au (s)
B. 1 g of Na (s)
C. 1 g of Li (s)
D. 1 g of Cl₂ (g)
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Answer: C. 1 g of Li (s)
Explanation: Lithium has the smallest atomic mass (7 g/mol), giving it the highest number of moles and thus the most atoms per gram.
18. Sum of mole fractions of all components in a solution is always equal to:
A. 1
B. 0
C. 100
D. Infinity
Show Answer
Answer: A. 1
Explanation: The total sum of the mole fractions of all constituent components in a mixture or solution equals unity (1).
19. How many moles of methane are required to produce 22 g of CO₂ upon complete combustion?
A. 0.5 mol
B. 1.0 mol
C. 2.0 mol
D. 0.25 mol
Show Answer
Answer: A. 0.5 mol
Explanation: CH₄ + 2O₂ → CO₂ + 2H₂O. 1 mole CH₄ gives 44g CO₂. Thus, 22g CO₂ requires 0.5 mole CH₄.
20. Express the number 0.000045 in scientific notation:
A. 4.5 × 10⁻⁵
B. 4.5 × 10⁻⁴
C. 45 × 10⁻⁶
D. 0.45 × 10⁻⁴
Show Answer
Answer: A. 4.5 × 10⁻⁵
Explanation: Moving the decimal point 5 places to the right yields 4.5 × 10⁻⁵.
21. The mass of 0.5 moles of N₂ gas is:
A. 14 g
B. 28 g
C. 7 g
D. 56 g
Show Answer
Answer: A. 14 g
Explanation: Molar mass of N₂ = 28 g/mol. Mass = 0.5 × 28 = 14 g.
22. Law of Conservation of Mass was given by:
A. Antoine Lavoisier
B. Joseph Proust
C. John Dalton
D. Gay-Lussac
Show Answer
Answer: A. Antoine Lavoisier
Explanation: Antoine Lavoisier established the Law of Conservation of Mass in 1789.
23. Which concentration unit is defined as moles of solute per liter of solution?
A. Molarity
B. Molality
C. Mole fraction
D. Normality
Show Answer
Answer: A. Molarity
Explanation: Molarity (M) = Moles of Solute / Volume of Solution in Liters.
24. What is the formula mass of NaCl? (Na = 23, Cl = 35.5)
A. 58.5 u
B. 58.0 u
C. 23.0 u
D. 35.5 u
Show Answer
Answer: A. 58.5 u
Explanation: Formula mass = 23 + 35.5 = 58.5 u.
25. Number of molecules present in 18 mg of water is:
A. 6.022 × 10²⁰
B. 6.022 × 10²³
C. 6.022 × 10²¹
D. 3.011 × 10²⁰
Show Answer
Answer: A. 6.022 × 10²⁰
Explanation: Moles = 0.018 g / 18 g/mol = 10⁻³ mol. Molecules = 10⁻³ × 6.022 × 10²³ = 6.022 × 10²⁰.
26. Which of the following is an intensive property?
A. Temperature
B. Mass
C. Volume
D. Enthalpy
Show Answer
Answer: A. Temperature
Explanation: Intensive properties do not depend on the quantity of matter present in the system.
27. What is the number of atoms present in 1 mole of oxygen gas (O₂)?
A. 1.2044 × 10²⁴
B. 6.022 × 10²³
C. 3.011 × 10²³
D. 1.2044 × 10²³
Show Answer
Answer: A. 1.2044 × 10²⁴
Explanation: 1 mole O₂ has 2 moles of O atoms = 2 × 6.022 × 10²³ = 1.2044 × 10²⁴ atoms.
28. Molecular formula is related to empirical formula by which relation?
A. Molecular Formula = n × Empirical Formula
B. Empirical Formula = n × Molecular Formula
C. Molecular Formula = Empirical Formula / n
D. Molecular Formula = Empirical Formula + n
Show Answer
Answer: A. Molecular Formula = n × Empirical Formula
Explanation: Where 'n' is an integer obtained by dividing Molecular Mass by Empirical Formula Mass.
29. Equal volumes of all gases under similar conditions of temperature and pressure contain equal number of molecules. This statement is:
A. Avogadro's Law
B. Gay-Lussac's Law
C. Boyle's Law
D. Charles' Law
Show Answer
Answer: A. Avogadro's Law
Explanation: Proposed by Amedeo Avogadro in 1811, this principle relates volume and mole numbers for gases.
30. What is the mass of 11.2 liters of CO₂ gas at STP?
A. 22 g
B. 44 g
C. 11 g
D. 88 g
Show Answer
Answer: A. 22 g
Explanation: 22.4 L of CO₂ at STP = 44 g (1 mol). Therefore, 11.2 L (0.5 mol) = 22 g.
