“Mole Concept” MCQ with Answer Explanation : NEET 2025.

40. What is the mass of 2 moles of MgO (Molar mass = 40 g/mol)?
    a) 80 g
    b) 60 g
    c) 20 g
    d) 40 g

Answer: a) 80 g

Explanation: 2 moles × 40 g/mol = 80 g.

41. The number of moles in 32 g of O₂ is:
    a) 1 mole
    b) 2 moles
    c) 0.5 moles
    d) 4 moles

Answer: a) 1 mole

Explanation: 32 g ÷ 32 g/mol = 1 mole.

42. If the molar mass of an unknown gas is 44 g/mol, how many moles are in 88 g?
    a) 2 moles
    b) 1 mole
    c) 4 moles
    d) 3 moles

Answer: a) 2 moles

Explanation: 88 g ÷ 44 g/mol = 2 moles.

43. How many moles are present in 5 g of NaCl (Molar mass = 58.5 g/mol)?
    a) 0.085 moles
    b) 0.1 moles
    c) 0.25 moles
    d) 0.3 moles

Answer: a) 0.085 moles

Explanation: 5 g ÷ 58.5 g/mol ≈ 0.085 moles.

44. In the equation 2Al + 3Cl₂ → 2AlCl₃, what is the mole ratio of aluminum to aluminum chloride?
    a) 1:2
    b) 2:3
    c) 2:2
    d) 3:2

Answer: a) 1:2

Explanation: The coefficients indicate that 2 moles of aluminum produce 2 moles of aluminum chloride.

45. Which of the following is a physical change?
    a) Combustion of gasoline
    b) Dissolving sugar in water
    c) Rusting of iron
    d) Baking bread

Answer: b) Dissolving sugar in water

Explanation: Dissolving sugar is a physical change since the substance remains chemically the same.

46. The term “mole” was first introduced by:
    a) Avogadro
    b) Dalton
    c) Gay-Lussac
    d) Boyle

Answer: a) Avogadro

Explanation: Avogadro introduced the concept of the mole in relation to the number of particles in a gas.

47. In a mixture of gases, if the mole fraction of gas A is 0.25, what is the partial pressure of gas A if the total pressure is 2 atm?
    a) 0.5 atm
    b) 1 atm
    c) 0.25 atm
    d) 0.75 atm

Answer: a) 0.5 atm

Explanation: Partial pressure = mole fraction × total pressure = 0.25 × 2 atm = 0.5 atm.

48. How many grams are in 1.5 moles of Na₂SO₄ (Molar mass = 142 g/mol)?
    a) 213 g
    b) 106 g
    c) 75 g
    d) 100 g

Answer: a) 213 g

Explanation: 1.5 moles × 142 g/mol = 213 g.

49. Which gas occupies a volume of 22.4 L at STP for 1 mole?
    a) O₂
    b) N₂
    c) CO₂
    d) All of the above

Answer: d) All of the above

Explanation: At STP, any ideal gas occupies 22.4 L for 1 mole.

50. In the reaction: 2H₂ + O₂ → 2H₂O, how many moles of O₂ are needed to react with 4 moles of H₂?
    a) 1 mole
    b) 2 moles
    c) 3 moles
    d) 4 moles

Answer: b) 2 moles

Explanation: The mole ratio shows that 2 moles of H₂ react with 1 mole of O₂; hence, 4 moles of H₂ need 2 moles of O₂.