In the depression of freezing point experiment
A. Vapour pressure of the solution is less than that of pure solvent
B. Vapour pressure of the solution is more than that of pure solvent
C. Only solute molecules solidify at the freezing point
D. Only solvent molecules solidify at the freezing point

In the depression of freezing point experiment, we analyze each statement:

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

This is TRUE. According to Raoult's law, the addition of a non-volatile solute lowers the vapour pressure of the solvent.

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

This is FALSE. It contradicts Raoult's law.

Statement C: Only solute molecules solidify at the freezing point.

This is FALSE. At the freezing point of a solution, it is the solvent that begins to solidify (separate out as pure solid), not the solute.

Statement D: Only solvent molecules solidify at the freezing point.

This is TRUE. When a solution reaches its freezing point, only the pure solvent crystallises out.

The correct statements are A and D.

The correct answer is Option A: A and D only.