Which of the following is a colligative property ?

Options

A. Lowering of vapour pressure
B. Osmotic pressure
C. Freezing point
D. Boiling point

Answer

To determine which of the given options is a colligative property, we need to understand what colligative properties are. Colligative properties are properties of solutions that depend on the number of solute particles in a given amount of solvent, rather than the identity of the solute.

### Step-by-Step Solution:

1. **Identify the Options**: The options given are:
- A) Lowering of vapor pressure
- B) Osmotic pressure
- C) Freezing point
- D) Boiling point

2. **Define Colligative Properties**: Colligative properties include:
- Lowering of vapor pressure
- Elevation of boiling point
- Depression of freezing point
- Osmotic pressure

3. **Analyze Each Option**:
- **Lowering of Vapor Pressure (Option A)**: This is a colligative property. When a non-volatile solute is added to a solvent, the vapor pressure decreases due to fewer solvent molecules escaping into the vapor phase.
- **Osmotic Pressure (Option B)**: This is also a colligative property. It depends on the concentration of solute particles in a solution and is defined as the pressure required to stop the flow of solvent into the solution through a semipermeable membrane.
- **Freezing Point (Option C)**: The freezing point itself is not a colligative property. However, the depression of freezing point (the lowering of the freezing point of a solvent upon the addition of a solute) is a colligative property.
- **Boiling Point (Option D)**: Similar to freezing point, the boiling point itself is not a colligative property, but the elevation of boiling point (the increase in boiling point of a solvent upon the addition of a solute) is a colligative property.

4. **Conclusion**: Based on the analysis, the colligative properties from the options provided are:
- A) Lowering of vapor pressure
- B) Osmotic pressure

Thus, the correct answers are A and B.

### Final Answer:
The colligative properties among the options are:
- A) Lowering of vapor pressure
- B) Osmotic pressure