Which of the following is not a colligative property ?

Options

A. Vapour pressure
B. Depression in f.pt.
C. Elevation in b.pt.
D. Osmotic pressure

Answer

To determine which of the following options 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 (moles) in a given amount of solvent, rather than the identity of the solute.

2. **List of Common Colligative Properties**:
- There are four main colligative properties:
1. **Relative Lowering of Vapor Pressure**: This property describes how the vapor pressure of a solvent decreases when a solute is added.
2. **Depression of Freezing Point**: This property describes how the freezing point of a solvent decreases when a solute is added.
3. **Elevation of Boiling Point**: This property describes how the boiling point of a solvent increases when a solute is added.
4. **Osmotic Pressure**: This property is related to the pressure required to stop the flow of solvent into a solution through a semipermeable membrane.

3. **Analyzing the Options**:
- We need to evaluate the options provided in the question to identify which one is not a colligative property.
- **Option A**: Relative lowering of vapor pressure - This is a colligative property.
- **Option B**: Depression of freezing point - This is a colligative property.
- **Option C**: Elevation of boiling point - This is a colligative property.
- **Option D**: Osmotic pressure - This is a colligative property.
- **Option E**: Vapor pressure - This is a general property of a liquid and does not depend on the number of solute particles.

4. **Conclusion**:
- Among the options, **vapor pressure** (Option E) is not a colligative property because it does not depend on the number of solute particles but rather on the nature of the solvent itself.

### Final Answer:
**The option that is not a colligative property is: Vapor Pressure.**

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