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Mole concept, molar mass and percentage composition: NEET MCQs with answers

111 questions on this topic of Some Basic Concepts in Chemistry (NEET 2027 syllabus). Here are 12; tap one to see its answer and explanation.

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easy

1. A specimen has mass 100 g and molar mass 80 g mol⁻¹. The number of moles present is:

  1. 0.8 mol
  2. 1.25 mol
  3. 2.5 mol
  4. 8000 mol
Show answer and explanation

Answer: (B) 1.25 mol

n = mass/molar mass = 100/80 = 1.25 mol.

Quick tip: Moles = mass ÷ molar mass.

medium

2. 22.4 L of any gas at STP contains:

  1. 6.022×10²³ atoms
  2. 6.022×10²³ molecules
  3. Avogadro's number of atoms
  4. Cannot determine atoms
Show answer and explanation

Answer: (D) Cannot determine atoms

22.4L = 1 mole molecules. Atoms = moles × atomicity. Atomicity varies per gas.

Quick tip: 22.4L = 1 mole molecules. But atoms depend on atomicity of the specific gas!

NCERT Class 11, Chapter 1, page 13

easy

3. The percentage by mass of nitrogen in NH₃ (molar mass 17 g/mol) is:

  1. 1.21 %
  2. 14 %
  3. 17.6 %
  4. 82.4 %
Show answer and explanation

Answer: (D) 82.4 %

% = (mass of nitrogen in one mole / molar mass) × 100 = 14/17 × 100 = 82.4%.

easy

4. Taking Nₐ = 6.022 × 10²³ mol⁻¹, the number of molecules in 20 g of NaOH (M = 40 g/mol) is:

  1. 1.51 × 10²³
  2. 1.2 × 10²⁵
  3. 6.02 × 10²³
  4. 3.01 × 10²³
Show answer and explanation

Answer: (D) 3.01 × 10²³

n = 20/40 = 0.5 mol; molecules = n × Nₐ = 3.01 × 10²³.

easy

5. 130 g of a substance with molar mass 20 g mol⁻¹ contains how many moles?

  1. 6.5 mol
  2. 0.154 mol
  3. 13 mol
  4. 2.6 mol
Show answer and explanation

Answer: (A) 6.5 mol

n = mass / molar mass = 130/20 = 6.5 mol.

Quick tip: n = m/M. Mass on top.

NCERT Class 11, Chapter 1

easy

6. The number of moles in 4 g of NaOH (molar mass 40 g/mol) is:

  1. 0.2 mol
  2. 10 mol
  3. 4 mol
  4. 0.1 mol
Show answer and explanation

Answer: (D) 0.1 mol

Number of moles = given mass/molar mass: n = 4/40 = 0.1 mol.

easy

7. Calculate the number of moles in a pure solid of mass 130 g whose molar mass is 100 g mol⁻¹.

  1. 1.3 mol
  2. 2.6 mol
  3. 13000 mol
  4. 0.769 mol
Show answer and explanation

Answer: (A) 1.3 mol

n = mass/molar mass = 130/100 = 1.3 mol.

Quick tip: Moles = mass ÷ molar mass.

easy

8. 80 g of a substance with molar mass 100 g mol⁻¹ contains how many moles?

  1. 0.8 mol
  2. 8 mol
  3. 1.25 mol
  4. 1.6 mol
Show answer and explanation

Answer: (A) 0.8 mol

n = mass / molar mass = 80/100 = 0.8 mol.

Quick tip: n = m/M. Mass on top.

NCERT Class 11, Chapter 1

easy

9. The number of moles in 490 g of H₂SO₄ (molar mass 98 g/mol) is:

  1. 490 mol
  2. 0.2 mol
  3. 5 mol
  4. 10 mol
Show answer and explanation

Answer: (C) 5 mol

Number of moles = given mass/molar mass: n = 490/98 = 5 mol.

easy

10. The number of moles in 9.8 g of H₂SO₄ (molar mass 98 g/mol) is:

  1. 9.8 mol
  2. 0.1 mol
  3. 10 mol
  4. 0.2 mol
Show answer and explanation

Answer: (B) 0.1 mol

Number of moles = given mass/molar mass: n = 9.8/98 = 0.1 mol.

easy

11. Taking Nₐ = 6.022 × 10²³ mol⁻¹, the number of molecules in 4 g of NaOH (M = 40 g/mol) is:

  1. 2.41 × 10²⁴
  2. 6.02 × 10²²
  3. 3.01 × 10²²
  4. 1.2 × 10²³
Show answer and explanation

Answer: (B) 6.02 × 10²²

n = 4/40 = 0.1 mol; molecules = n × Nₐ = 6.02 × 10²².

easy

12. Taking Nₐ = 6.022 × 10²³ mol⁻¹, the number of molecules in 80 g of NaOH (M = 40 g/mol) is:

  1. 4.82 × 10²⁵
  2. 2.41 × 10²⁴
  3. 1.2 × 10²⁴
  4. 6.02 × 10²³
Show answer and explanation

Answer: (C) 1.2 × 10²⁴

n = 80/40 = 2 mol; molecules = n × Nₐ = 1.2 × 10²⁴.

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