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

31. Which of the following indicates an increase in the number of moles?
    a) Combining two reactants to form one product
    b) Decomposing one reactant into multiple products
    c) Diluting a solution
    d) Evaporating a liquid

Answer: b) Decomposing one reactant into multiple products

Explanation: Decomposition typically increases the number of moles since one substance breaks into several.

32. In a mixture of gases, if the total pressure is 1 atm and the partial pressure of gas A is 0.3 atm, what is the mole fraction of gas A?
    a) 0.3
    b) 0.7
    c) 0.5
    d) 1.0

Answer: a) 0.3

Explanation: The mole fraction is the partial pressure divided by the total pressure: 0.3 atm ÷ 1 atm = 0.3.

33. How many grams are in 0.75 moles of NaOH (Molar mass = 40 g/mol)?
    a) 30 g
    b) 40 g
    c) 60 g
    d) 20 g

Answer: c) 30 g

Explanation: 0.75 moles × 40 g/mol = 30 g.

34. In a balanced equation, the coefficients represent:
    a) Mass ratios
    b) Mole ratios
    c) Volume ratios
    d) Energy ratios

Answer: b) Mole ratios

Explanation: The coefficients in a balanced equation indicate the relative number of moles of each substance involved in the reaction.

35. If the molar mass of a gas is 28 g/mol, how many grams are in 3 moles?
    a) 28 g
    b) 56 g
    c) 84 g
    d) 92 g

Answer: c) 84 g

Explanation: 3 moles × 28 g/mol = 84 g.

36. In the reaction: 2C₃H₈ + 7O₂ → 6CO₂ + 8H₂O, what is the mole ratio of propane to water?
    a) 1:4
    b) 2:8
    c) 1:3
    d) 2:4

Answer: b) 2:8

Explanation: The balanced equation shows that 2 moles of propane produce 8 moles of water, which simplifies to 1:4.

37. The mass of 0.25 moles of KNO₃ (Molar mass = 101 g/mol) is:
    a) 25.25 g
    b) 20.25 g
    c) 25 g
    d) 30.25 g

Answer: a) 25.25 g

Explanation: 0.25 moles × 101 g/mol = 25.25 g.

38. In a chemical equation, if the coefficients are doubled, what happens to the number of moles of each reactant and product?
    a) Doubled
    b) Halved
    c) Remains the same
    d) Tripled

Answer: a) Doubled

Explanation: Doubling the coefficients in a balanced equation doubles the moles of each substance.

39. How many molecules are in 0.5 moles of H₂O?
    a) 6.022 × 10²³
    b) 3.011 × 10²³
    c) 1.2044 × 10²³
    d) 1.5 × 10²²

Answer: b) 3.011 × 10²³

Explanation: 0.5 moles × 6.022 × 10²³ molecules/mole = 3.011 × 10²³ molecules.