Which of the following is not a colligative property ?

Options

A. Osmotic pressure
B. Boiling point
C. Vapour pressure
D. Electrical conductivity

Answer

To determine which of the following is not a colligative property, we first need to understand what colligative properties are.

### Step-by-Step Solution:

1. **Definition of Colligative Properties**:
- Colligative properties are properties of solutions that depend on the number of solute particles in a given amount of solvent, regardless of the nature of the solute.

2. **List of Common Colligative Properties**:
- **Osmotic Pressure**: The pressure required to stop the flow of solvent into a solution through a semipermeable membrane.
- **Elevation in Boiling Point**: The increase in boiling point of a solvent when a solute is dissolved in it (ΔTb).
- **Depression in Freezing Point**: The decrease in freezing point of a solvent when a solute is dissolved in it (ΔTf).
- **Relative Lowering of Vapor Pressure**: The decrease in vapor pressure of a solvent when a solute is added.

3. **Identify the Options**:
- Now, we need to identify the options given in the question. Typically, the options would include various properties, among which we need to find the one that is not a colligative property.

4. **Analyzing Each Option**:
- **Option 1**: Osmotic Pressure - This is a colligative property.
- **Option 2**: Elevation in Boiling Point - This is a colligative property.
- **Option 3**: Depression in Freezing Point - This is a colligative property.
- **Option 4**: Electrical Conductivity - This property depends on the nature of the solute and its ability to conduct electricity, rather than just the number of solute particles.

5. **Conclusion**:
- Since electrical conductivity depends on the nature of the solute and not merely on the number of solute particles, it is not a colligative property. Therefore, the correct answer is **Electrical Conductivity**.

### Final Answer:
**Electrical Conductivity is not a colligative property.**