Free Moles and Avogadro's Number MCQs with Answers

117 Moles and Avogadro's Number MCQs from Chemistry, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.

The mole connects the microscopic number of particles with measurable mass, using Avogadro's number, 6.022 × 10²³ particles per mole. Questions involve molar mass, conversion between mass, moles and particles, percentage composition, empirical and molecular formulas, and distinguishing atoms, molecules, ions and formula units.

Last updated 9 September 2026

117 questions · page 1 of 6

1. The value of Avogadro's number is

A. 6.02 x 10^-23
B. 6.02 x 10^23
C. 6.02 x 10^24
D. 3.01 x 10^23

Explanation: One mole of any substance contains 6.02 x 10^23 particles, whether those particles are atoms, molecules or ions.

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2. One mole of a substance is defined as

A. the amount containing as many particles as there are atoms in 12 g of carbon 12
B. one gram of the substance
C. the mass of one molecule of the substance
D. the volume occupied by one gram of a gas

Explanation: The mole is a counting unit fixed by reference to 12 g of carbon 12, which is why the molar mass of any substance in grams contains…

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3. The number of moles present in 36 g of water is

A. 0.5
B. 1
C. 2
D. 18

Explanation: The molar mass of water is 2(1) + 16, that is 18 g per mole, so 36 divided by 18 gives 2 moles.

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4. The number of molecules in 2 moles of carbon dioxide is

Moderate

A. 6.02 x 10^23
B. 3.01 x 10^23
C. 44
D. 1.204 x 10^24

Explanation: Two moles contain 2 x 6.02 x 10^23, which is 1.204 x 10^24 molecules, and this is true for any substance since the mole counts particles…

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5. The volume occupied by one mole of any ideal gas at standard temperature and pressure is

A. 22.4 dm3
B. 24 dm3
C. 1 dm3
D. 22.4 cm3

Explanation: At 273 K and 1 atmosphere one mole of any gas occupies 22.4 dm3, which follows from the ideal gas equation and is independent of the…

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6. The mass of 0.5 mole of sodium hydroxide, NaOH, is

A. 40 g
B. 20 g
C. 80 g
D. 10 g

Explanation: The molar mass is 23 + 16 + 1, that is 40 g per mole, so half a mole has a mass of 20 g.

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7. The total number of atoms present in one mole of sulphuric acid, H2SO4, is

A. 6.02 x 10^23
B. 4.21 x 10^24
C. 4.214 x 10^24
D. 98

Explanation: One molecule contains 2 + 1 + 4, that is 7 atoms, so one mole contains 7 x 6.02 x 10^23, which is 4.214 x 10^24 atoms.

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8. A compound has the empirical formula CH2O and a relative molecular mass of 180. Its molecular formula is

A. CH2O
B. C2H4O2
C. C3H6O3
D. C6H12O6

Explanation: The empirical formula mass is 12 + 2 + 16, that is 30, and 180 divided by 30 gives 6, so every subscript is multiplied by six to give…

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9. The percentage by mass of carbon in carbon dioxide, CO2, is about

Hard

A. 27.3 per cent
B. 12 per cent
C. 44 per cent
D. 72.7 per cent

Explanation: The molar mass is 12 + 32, that is 44, so the carbon fraction is 12 divided by 44 multiplied by 100, giving 27.3 per cent.

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10. The molar mass of carbon dioxide, CO2, is

A. 44 g per mole
B. 28 g per mole
C. 12 g per mole
D. 32 g per mole

Explanation: Adding one carbon at 12 and two oxygens at 16 each gives 12 + 32, that is 44 g per mole.

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11. The relative atomic mass of an element is

Moderate

A. the mass in grams of one atom of the element
B. the average mass of its atoms compared with one twelfth the mass of a carbon 12 atom
C. the number of protons in its nucleus
D. always a whole number

Explanation: Relative atomic mass is a ratio, so it has no units, and it is an average weighted by the natural abundance of the isotopes.

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12. The molarity of a solution is defined as the number of moles of solute dissolved in

Very hard

A. 1000 g of solvent
B. one litre of solvent
C. one cubic decimetre of solution
D. one mole of solvent

Explanation: Molarity refers to the total volume of the final solution, not to the volume of solvent used, which is why a standard solution is made up…

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13. Which of the following samples contains the greatest number of atoms?

A. 1 mole of helium gas
B. 1 mole of oxygen gas, O2
C. 1 mole of water, H2O
D. 1 mole of ammonia, NH3

Explanation: Every sample contains one mole of molecules, so the answer depends on the number of atoms in each molecule: helium has one, oxygen two…

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14. Consider the equation H2 + O2 gives H2O. What volume of hydrogen gas is required to produce 1 mol of water at standard temperature and pressure?

A. 11.2 dm3
B. 22.4 dm3
C. 10 dm3
D. 58 dm3

Explanation: Balanced properly the equation is 2H2 plus O2 giving 2H2O, so one mole of water needs one mole of hydrogen, and one mole of any gas…

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15. 4moles of Carbon dioxide(CO2) have _____molecules.

A. 6.02 x 10^23
B. 12.04 x 10^25
C. 18.06 x 10^23
D. 24.08 x 10^23

Explanation: One mole contains 6.022 x 10^23 molecules, so 4 moles contain 4 x 6.022 x 10^23 = 24.088 x 10^23 molecules, which is approximately 24.08 x…

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16. Identify the Molecular mass for Glucose (C6H12O6) among the following.

A. 190amu
B. 188amu
C. 180amu
D. 98amu

Explanation: The molecular mass of glucose is calculated as (6 x 12 amu) + (12 x 1 amu) + (6 x 16 amu) = 72 amu + 12 amu + 96 amu = 180 amu.

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17. The molecular formula of Glucose is____________?

A. NH3
B. C12H22O11
C. C6H12O6
D. C6H6

Explanation: Glucose is a monosaccharide with the molecular formula C6H12O6, showing six carbon atoms, twelve hydrogen atoms, and six oxygen atoms in…

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18. The molecular formula of Sucrose(Sugar) is___________?

A. NH3
B. C12H22O11
C. C6H12O6
D. C6H6

Explanation: Sucrose is a disaccharide formed from glucose and fructose, with the molecular formula C12H22O11 after loss of water during condensation.

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19. The number of moles are present in 9.5g of CS2?

A. 1.5
B. 0.25
C. 0.125
D. None of These

Explanation: The molar mass of CS2 is 12 g/mol + (2 x 32 g/mol) = 76 g/mol. Therefore, moles = mass/molar mass = 9.5 g / 76 g/mol = 0.125 mol.

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20. The one mole of _____molecule has the highest number of atoms?

A. H2SO4
B. HClO4
C. O3
D. H2C2O4

Explanation: One mole of each compound contains the same number of molecules, so compare atoms in one molecule: H2SO4 has 7 atoms, HClO4 has 6, O3 has…

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