In the depression of freezing point experiment, it is found that the:

Options

A. vapour pressure of pure solvent is more than that of solution
B. vapour pressure of pure solvent is less than that of solution
C. only solute molecules solidify at the freezing point
D. only solvent molecules solidify at the freezing point

Answer

To solve the question regarding the depression of freezing point experiment, we need to analyze the given options based on the principles of colligative properties. Here’s a step-by-step breakdown:

### Step 1: Understand the Concept of Freezing Point Depression
Freezing point depression is a colligative property that occurs when a non-volatile solute is added to a solvent. This results in a decrease in the freezing point of the solvent.

### Step 2: Analyze the Effect on Vapor Pressure
When a non-volatile solute is added to a pure solvent, the vapor pressure of the solution decreases compared to that of the pure solvent. This is because the solute particles occupy some of the surface area, reducing the number of solvent molecules that can escape into the vapor phase.

### Step 3: Evaluate the Options
1. **Option A**: Vapor pressure of the pure solvent is more than that of the solution.
- This statement is **true** because the addition of a non-volatile solute lowers the vapor pressure of the solution compared to that of the pure solvent.

2. **Option B**: Vapor pressure of the pure solvent is less than that of the solution.
- This statement is **false** because we established that the vapor pressure of the pure solvent is higher than that of the solution.

3. **Option C**: Only solute molecules solidify at the freezing point.
- This statement is **false** because at the freezing point, it is the solvent that solidifies, not the solute. The solute remains in solution as it is non-volatile.

4. **Option D**: Only solvent molecules solidify at the freezing point.
- This statement is **true** because during the freezing of the solution, only the solvent molecules form a solid phase while the solute remains dissolved.

### Conclusion
Based on the analysis:
- The correct answers are **Option A** and **Option D**.