In the depression of freezing point experimet, it is found that:
I. The vapour pressure of the solution is less than that of pure solvent.
II. The vapour pressure of the solution is more than that of pure solvent.
III. Only solute molecules solidify at the freezing point.
IV. Only solvent molecules solidify at the freezing point.

Options

A. I,II
B. II,III
C. I,IV
D. I,II,III.

Explanation

To solve the question regarding the depression of freezing point experiment, we need to analyze each of the four statements provided:

1. **Statement I**: The vapor pressure of the solution is less than that of pure solvent.
- In a solution, the presence of solute particles lowers the vapor pressure of the solvent. This is due to the solute particles occupying space at the surface of the liquid, reducing the number of solvent molecules that can escape into the vapor phase. Therefore, this statement is **correct**.

2. **Statement II**: The vapor pressure of the solution is more than that of pure solvent.
- This statement contradicts the principle of vapor pressure lowering in solutions. Since the vapor pressure of the solution is lower than that of the pure solvent due to the presence of solute, this statement is **incorrect**.

3. **Statement III**: Only solute molecules solidify at the freezing point.
- In a solution, when freezing occurs, it is primarily the solvent that solidifies. Solute particles do not solidify because they are non-volatile and remain in the solution. Hence, this statement is **incorrect**.

4. **Statement IV**: Only solvent molecules solidify at the freezing point.
- This statement is correct. During the freezing process, it is the solvent that crystallizes into a solid form, while the solute remains dissolved in the liquid phase. Therefore, this statement is **correct**.

Based on the analysis above, the correct answer is **Statement IV**: Only solvent molecules solidify at the freezing point.

### Summary of the Solution Steps:
1. Analyze Statement I: Correct, vapor pressure of solution is less than that of pure solvent.
2. Analyze Statement II: Incorrect, vapor pressure of solution cannot be more than that of pure solvent.
3. Analyze Statement III: Incorrect, only solvent solidifies, not solute.
4. Analyze Statement IV: Correct, only solvent molecules solidify at the freezing point.