Concept of freezing point depression

When a non-volatile solute is dissolved in a solvent:

• the vapour pressure of the solution decreases compared to the pure solvent,
• the freezing point of the solution decreases.

Check statement A

Statement A: Vapour pressure of the solution is less than that of pure solvent

This is true by Raoult’s law: $P_{\text{solution}} < P_{\text{pure solvent}}$

Check statement B

Statement B: Vapour pressure of the solution is more than that of pure solvent

This is the opposite of the correct fact, so false.

Check statement C

Statement C: Only solute molecules solidify at the freezing point

This is false. In freezing point depression, the solid phase that separates is essentially the pure solvent, not the solute.

Check statement D

Statement D: Only solvent molecules solidify at the freezing point

This is true. At the freezing point, the solvent crystallizes out first.

Select the correct option

True statements are A and D only.

Therefore, the correct option is: $\boxed{\text{C}}$

Comparison with stored answer

Stored correct answer: C

Our derived answer: C

So, they agree.