Which is not a colligative property?

Options

A. Lowering of vapour pressure
B. Freezing point
C. Osmotic pressure
D. Elevation in boiling point

Explanation

To determine which property 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 (ions or molecules) in a given amount of solvent, rather than the identity of the solute.

2. **List of Common Colligative Properties**:
- The main colligative properties include:
- Relative lowering of vapor pressure
- Elevation of boiling point
- Depression of freezing point
- Osmotic pressure

3. **Understanding Lowering of Vapor Pressure**:
- Lowering of vapor pressure refers to the decrease in vapor pressure of a solvent when a non-volatile solute is added. However, this term alone does not specify the relationship to the mole fraction of the solvent or solute.

4. **Relative Lowering of Vapor Pressure**:
- The relative lowering of vapor pressure is defined as the change in vapor pressure (ΔP) divided by the original vapor pressure (P). This ratio depends on the mole fraction of the solute and is a colligative property.

5. **Identifying the Non-Colligative Property**:
- The question asks for a property that is not a colligative property. Since "lowering of vapor pressure" does not take into account the mole fraction and is not expressed as a ratio, it does not qualify as a colligative property.

6. **Conclusion**:
- Therefore, the correct answer is that "lowering of vapor pressure" is not a colligative property.

### Final Answer:
The property that is not a colligative property is **lowering of vapor pressure**.

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