Which is not a colligative property?

Options

A. Osmotic pressure
B. Lowering in vapour pressure
C. Depression in freezing point
D. Refractive index

Answer

To determine which property is not a colligative property, we first need to understand what colligative properties are. Colligative properties depend on the number of solute particles in a solution and not on the nature of the solute. The main colligative properties include:

1. **Relative Lowering of Vapor Pressure**: When a non-volatile solute is added to a solvent, the vapor pressure of the solvent decreases. This is a colligative property.

2. **Elevation in Boiling Point**: The boiling point of a solvent increases when a non-volatile solute is added. This is also a colligative property.

3. **Depression in Freezing Point**: The freezing point of a solvent decreases when a non-volatile solute is added. This is another colligative property.

4. **Osmotic Pressure**: This is the pressure required to stop the flow of solvent into a solution through a semipermeable membrane. It is also a colligative property.

Now, we need to identify which of the given options is not a colligative property. The options typically include:

- Relative Lowering of Vapor Pressure
- Elevation in Boiling Point
- Depression in Freezing Point
- Refractive Index

Among these, the refractive index is a measure of how much light is bent, or refracted, when entering a material. It is dependent on the nature of the substance and does not depend solely on the number of solute particles in a solution. Therefore, the refractive index is not a colligative property.

**Final Answer**: The property that is not a colligative property is the **Refractive Index**.

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