Which is not a colligative property?

Options

A. Relative lowering of vapour pressure
B. Freezing point
C. Osmotic pressure
D. Elevation of boiling point

Answer

To determine which of the given 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 in a given amount of solvent, rather than the identity of the solute.

2. **Common Colligative Properties**:
- The main colligative properties include:
- Relative Lowering of Vapor Pressure
- Depression of Freezing Point
- Elevation of Boiling Point
- Osmotic Pressure

3. **Analyzing the Options**:
- We need to identify which of the listed properties does not fit the definition of colligative properties.
- The first three properties (Relative Lowering of Vapor Pressure, Depression of Freezing Point, and Elevation of Boiling Point) are all dependent on the number of solute particles.

4. **Understanding Osmotic Pressure**:
- Osmotic pressure is the pressure required to stop the flow of solvent into a solution through a semipermeable membrane.
- While osmotic pressure does depend on the concentration of solute particles, it is not considered a colligative property in the traditional sense because it involves a pressure difference rather than just the number of solute particles.

5. **Conclusion**:
- Based on the definitions and analysis, osmotic pressure is the property that does not fit the criteria of a colligative property. Therefore, the answer to the question is that osmotic pressure is not a colligative property.

### Final Answer:
Osmotic pressure is not a colligative property.

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