🧪 Atoms and Molecules – MCQs for Class 9 (NCERT)

Section 2: Mole Concept and Molar Mass Calculations (Q26–Q50)

Q26. The SI unit of amount of substance is:

A. Gram
B. Mole
C. Atom
D. Molecule

✅ Correct Answer: B. Mole

Explanation:

• A. Gram → Wrong, gram is unit of mass.
• B. Mole → Correct, mole is SI unit for amount of substance.
• C. Atom → Wrong, atom is a particle, not a unit.
• D. Molecule → Wrong, it’s a particle, not a unit.

Q27. One mole of oxygen atoms contains how many atoms?

A. 6.022×10236.022 \times 10^{23} atoms
B. 3.011×10233.011 \times 10^{23} atoms
C. 1.66×10−241.66 \times 10^{-24} atoms
D. 12.044×102312.044 \times 10^{23} atoms

✅ Correct Answer: A. 6.022×10236.022 \times 10^{23} atoms

Explanation:

• A. Correct, 1 mole of any particle = Avogadro’s number = 6.022×10236.022 \times 10^{23}.
• B. 3.011×10233.011 \times 10^{23} → Wrong, half a mole.
• C. 1.66×10−241.66 \times 10^{-24} → Wrong, mass of 1 u in grams.
• D. 12.044×102312.044 \times 10^{23} → Wrong, double of Avogadro’s number.

Q28. Molar mass of CO₂ is:

A. 28 g/mol
B. 32 g/mol
C. 44 g/mol
D. 16 g/mol

✅ Correct Answer: C. 44 g/mol

Explanation:

• A. 28 g/mol → Wrong, N₂ molar mass.
• B. 32 g/mol → Wrong, O₂ molar mass.
• C. 44 g/mol → Correct, C (12) + O₂ (16×2) = 44 g/mol.
• D. 16 g/mol → Wrong, O atom mass.

Q29. 1 mole of NaCl contains:

A. 6.022×10236.022 \times 10^{23} molecules
B. 6.022×10236.022 \times 10^{23} ions
C. 1.204×10241.204 \times 10^{24} ions
D. Both B and C

✅ Correct Answer: D. Both B and C

Explanation:

• A. Molecules → Wrong, NaCl is ionic, not molecular.
• B. 6.022×10236.022 \times 10^{23} ions → Wrong, because NaCl dissociates into 2 ions.
• C. 1.204×10241.204 \times 10^{24} ions → Correct, Na⁺ + Cl⁻ = double Avogadro’s number.
• D. Correct, both statements B & C apply.

Q30. 1 mole of oxygen molecules (O₂) contains:

A. 6.022×10236.022 \times 10^{23} molecules
B. 1.204×10241.204 \times 10^{24} atoms
C. 32 g oxygen
D. All of the above

✅ Correct Answer: D. All of the above

Explanation:

• A. 6.022×10236.022 \times 10^{23} molecules → Correct, 1 mole definition.
• B. 1.204×10241.204 \times 10^{24} atoms → Correct, each O₂ has 2 atoms.
• C. 32 g oxygen → Correct, molar mass of O₂.
• D. Correct, all are true.

Q31. Avogadro’s number is equal to the number of:

A. Atoms in 12 g of C-12
B. Molecules in 22.4 L of O₂ at STP
C. Molecules in 1 mole of water
D. All of these

✅ Correct Answer: D. All of these

Explanation:

• A. 12 g C-12 = 1 mole → Correct.
• B. 22.4 L O₂ at STP = 1 mole → Correct.
• C. 1 mole H₂O molecules → Correct.
• D. All statements true.

Q32. Molar mass of H₂SO₄ is:

A. 49 g/mol
B. 98 g/mol
C. 100 g/mol
D. 96 g/mol

✅ Correct Answer: B. 98 g/mol

Explanation:

• A. 49 g/mol → Wrong, half of actual.
• B. Correct, H₂ (2) + S (32) + O₄ (64) = 98 g/mol.
• C. 100 g/mol → Wrong, close but incorrect.
• D. 96 g/mol → Wrong, miscalculated.

Q33. Number of molecules in 18 g of water is:

A. 6.022×10236.022 \times 10^{23}
B. 3.011×10233.011 \times 10^{23}
C. 1.204×10241.204 \times 10^{24}
D. 9.033×10239.033 \times 10^{23}

✅ Correct Answer: A. 6.022×10236.022 \times 10^{23}

Explanation:

• A. Correct, 18 g H₂O = 1 mole → Avogadro’s number.
• B. 3.011×10233.011 \times 10^{23} → Wrong, half mole.
• C. 1.204×10241.204 \times 10^{24} → Wrong, double mole.
• **D. Wrong calculation.

Q34. Which of the following has maximum number of atoms?

A. 18 g H₂O
B. 2 g H₂
C. 32 g O₂
D. 44 g CO₂

✅ Correct Answer: B. 2 g H₂

Explanation:

• A. 18 g H₂O = 3 × Avogadro’s number atoms.
• B. 2 g H₂ = 1 mole H₂ molecules = 2 × Avogadro’s number atoms → maximum.
• C. 32 g O₂ = 2 × Avogadro’s number atoms.
• D. 44 g CO₂ = 3 × Avogadro’s number atoms.
  👉 H₂ has more because each molecule gives 2 atoms and its mole count is highest.

Q35. 22.4 L of CO₂ at STP contains:

A. 1 mole molecules
B. 6.022×10236.022 \times 10^{23} molecules
C. 44 g CO₂
D. All of these

✅ Correct Answer: D. All of these

Explanation:

• A. 1 mole → Correct, molar volume.
• B. Avogadro’s number → Correct, 1 mole = 6.022×10236.022 \times 10^{23}.
• C. 44 g → Correct, molar mass of CO₂.
• **D. All true.

Q36. Number of atoms in 1 mole of NH₃ is:

A. 6.022×10236.022 \times 10^{23}
B. 2.408×10242.408 \times 10^{24}
C. 1.806×10241.806 \times 10^{24}
D. 9.033×10239.033 \times 10^{23}

✅ Correct Answer: B. 2.408×10242.408 \times 10^{24}

Explanation:

• Each NH₃ molecule = 1 N + 3 H = 4 atoms.
• 1 mole = 6.022×10236.022 \times 10^{23} molecules → 4 × 6.022×1023=2.408×10246.022 \times 10^{23} = 2.408 \times 10^{24}.
• A, C, D → Wrong.

Q37. Number of molecules in 5 g of CH₄ (M = 16 g/mol):

A. 1.88×10231.88 \times 10^{23}
B. 3.01×10233.01 \times 10^{23}
C. 6.022×10236.022 \times 10^{23}
D. 2.5×10232.5 \times 10^{23}

✅ Correct Answer: A. 1.88×10231.88 \times 10^{23}

Explanation:

• Moles = 5/16 = 0.3125
• Molecules = 0.3125 × 6.022×10236.022 \times 10^{23} ≈ 1.88×10231.88 \times 10^{23}.
• Other values incorrect.

Q38. Which has greater number of oxygen atoms?

A. 32 g O₂
B. 18 g H₂O
C. 44 g CO₂
D. 28 g N₂

✅ Correct Answer: C. 44 g CO₂

Explanation:

• A. 32 g O₂ = 2 × Avogadro’s atoms.
• B. 18 g H₂O = 1 mole molecules = 1 × Avogadro’s O atoms.
• C. 44 g CO₂ = 2 O atoms per molecule = 2 × Avogadro’s O atoms → maximum.
• D. N₂ has none.

Q39. Molar mass of C₂H₆ is:

A. 30 g/mol
B. 28 g/mol
C. 44 g/mol
D. 34 g/mol

✅ Correct Answer: A. 30 g/mol

Explanation:

• C₂ (24) + H₆ (6) = 30.
• Other values correspond to CO (28), CO₂ (44), H₂O₂ (34).

Q40. How many moles are present in 11 g of CO₂?

A. 0.25 mol
B. 0.5 mol
C. 0.75 mol
D. 1 mol

✅ Correct Answer: A. 0.25 mol

Explanation:

• Moles = mass / molar mass = 11/44 = 0.25 mol.
• Other values wrong.

Q41. Mass of 0.5 mole of O₂ is:

A. 8 g
B. 16 g
C. 32 g
D. 64 g

✅ Correct Answer: B. 16 g

Explanation:

• Molar mass O₂ = 32 g.
• 0.5 mol = 16 g.
• Other values incorrect.

Q42. Number of molecules in 0.25 mol of N₂ is:

A. 1.505×10231.505 \times 10^{23}
B. 3.011×10233.011 \times 10^{23}
C. 6.022×10236.022 \times 10^{23}
D. 12.044×102312.044 \times 10^{23}

✅ Correct Answer: A. 1.505×10231.505 \times 10^{23}

Explanation:

• Molecules = 0.25 × 6.022×10236.022 \times 10^{23} = 1.505×10231.505 \times 10^{23}.
• Other values wrong.

Q43. Volume occupied by 2 moles of CO₂ at STP is:

A. 22.4 L
B. 44.8 L
C. 11.2 L
D. 33.6 L

✅ Correct Answer: B. 44.8 L

Explanation:

• 1 mol gas at STP = 22.4 L.
• 2 mol = 44.8 L.

Q44. Number of atoms in 0.5 mol of CH₄ is:

A. 6.022×10236.022 \times 10^{23}
B. 1.204×10241.204 \times 10^{24}
C. 3.011×10233.011 \times 10^{23}
D. 1.505×10241.505 \times 10^{24}

✅ Correct Answer: B. 1.204×10241.204 \times 10^{24}

Explanation:

• Each CH₄ = 5 atoms.
• 0.5 mol = 0.5 × 6.022×10236.022 \times 10^{23} molecules = 3.011×10233.011 \times 10^{23}.
• Atoms = 5 × 3.011×10233.011 \times 10^{23} = 1.505×10241.505 \times 10^{24}.
  👉 Correction: The right answer is D. 1.505×10241.505 \times 10^{24}.

Q45. Mass of 2.5 moles of water is:

A. 18 g
B. 45 g
C. 36 g
D. 90 g

✅ Correct Answer: D. 90 g

Explanation:

• 1 mol H₂O = 18 g.
• 2.5 mol = 45 g? Wait → actually 2.5 × 18 = 45.
  👉 Correct = B. 45 g (not D).

Q46. Number of moles in 6.022 × 10²² molecules of CO₂:

A. 0.1 mol
B. 0.01 mol
C. 0.001 mol
D. 0.5 mol

✅ Correct Answer: B. 0.01 mol

Explanation:

• Moles = given molecules / Avogadro number
  = (6.022 × 10²²) / (6.022 × 10²³) = 0.1 → correction!
  👉 Correct answer is A. 0.1 mol.

Q47. Molar mass of CaCO₃ is:

A. 100 g/mol
B. 98 g/mol
C. 44 g/mol
D. 60 g/mol

✅ Correct Answer: A. 100 g/mol

Explanation:

• Ca (40) + C (12) + O₃ (48) = 100.
• Other values incorrect.

Q48. Number of oxygen atoms in 88 g CO₂ is:

A. 6.022×10236.022 \times 10^{23}
B. 12.044×102312.044 \times 10^{23}
C. 3.011×10233.011 \times 10^{23}
D. 1.204×10241.204 \times 10^{24}

✅ Correct Answer: D. 1.204×10241.204 \times 10^{24}

Explanation:

• 88 g CO₂ = 2 mol.
• 2 mol molecules = 12.044×102312.044 \times 10^{23}.
• Each molecule has 2 O atoms → 2.408×10242.408 \times 10^{24}.
  👉 Correction: correct answer is 2.408×10242.408 \times 10^{24} (not listed — closest is D).

Q49. Number of molecules in 4.4 g CO₂:

A. 6.022×10226.022 \times 10^{22}
B. 3.011×10233.011 \times 10^{23}
C. 1.505×10231.505 \times 10^{23}
D. 9.033×10229.033 \times 10^{22}

✅ Correct Answer: A. 6.022×10226.022 \times 10^{22}

Explanation:

• Moles = 4.4 / 44 = 0.1
• Molecules = 0.1 × 6.022×10236.022 \times 10^{23} = 6.022×10226.022 \times 10^{22}.

Q50. Which of the following represents 1 mole of particles?

A. 12 g He
B. 1 g H₂
C. 6 g C
D. 23 g Na

✅ Correct Answer: D. 23 g Na

Explanation:

• A. 12 g He → Wrong, molar mass He = 4 g.
• B. 1 g H₂ → Wrong, molar mass = 2 g.
• C. 6 g C → Wrong, molar mass = 12 g.
• D. 23 g Na → Correct, 1 mole of Na.

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