Which of the following colligative property is associated with concentration in terms of molarity?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Osmotic pressure
Osmotic pressure is given by π = CRT, where C is the molarity (mol L−1) of the solution.
Why the other options are incorrect
Option (1) Lowering of vapour pressure — Incorrect. The relative lowering of vapour pressure equals the mole fraction of the solute (Δp/p° = x2).
Option (2) Depression in freezing point — Incorrect. ΔTf = Kfm, where m is the molality.
Option (4) Elevation in boiling point — Incorrect. ΔTb = Kbm, again in terms of molality.
NCERT (2026-27 edition):
Osmosis and Osmotic Pressure – “… The osmotic pressure method has the advantage over other methods as pressure measurement is around the room temperature and the molarity of the solution is used instead of molality. As compared to other colligative properties, its magnitude is large even for very dilute solutions.”