Which of the following is a colligative property?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Relative lowering of vapor pressure
Colligative properties depend only on the number of solute particles, not on their nature. For relative lowering of vapour pressure, Raoult’s law gives:
\( \displaystyle \frac{p_1^{\circ}-p_1}{p_1^{\circ}}=x_2 \)
It depends only on x2, the mole fraction of the solute, that is, on the number of solute particles. So relative lowering of vapour pressure is a colligative property.
Why the other options are incorrect
Option (1) Solubility — Incorrect. It depends on the nature of the solute and solvent (“like dissolves like”), so it is not colligative.
Option (3) Boiling point — Incorrect. The boiling point itself depends on the nature of the liquid. Only the elevation of boiling point (ΔTb) is colligative.
Option (4) Freezing point — Incorrect. Likewise, only the depression of freezing point (ΔTf) is colligative, not the freezing point itself.
NCERT (2026-27 edition):
Colligative Properties and Determination of Molar Mass
