Which of the following does not come under the category of colligative properties?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Depression in Freezing point of the solute
When a non-volatile solute is dissolved in a solvent, some properties of the solution depend only on the number of solute particles, not on their nature. These colligative properties are all properties of the solvent in the solution or of the solution itself.
Option (1) Relative lowering of vapor pressure — A colligative property. The fall in the vapour pressure of the solvent divided by the vapour pressure of the pure solvent equals the mole fraction of the solute.
Option (2) Osmotic pressure of solution — A colligative property. \( \pi = CRT \): it depends on the molar concentration of solute particles.
Option (3) Depression in Freezing point of the solvent — A colligative property. \( \Delta T_f = K_f\,m \): it is proportional to the molality of the solute particles.
Option (4) Depression in Freezing point of the solute — Not a colligative property. When a solution is cooled, it is the solvent that freezes out, at a lower temperature than the pure solvent. A “freezing point of the solute” is not a property of the solution at all.
NCERT (2026-27 edition):
Colligative Properties and Determination of Molar Mass – …
