Which one is a colligative property

Options

A. Boiling point
B. Vapour pressure
C. Osmotic pressure
D. Freezing point

Explanation

To determine which of the given options is a colligative property, we first need to understand what colligative properties are. 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 itself.

### Step-by-Step Solution:

1. **Identify the Options**: The options given are:
- Option 1: Boiling Point
- Option 2: Vapor Pressure
- Option 3: Osmotic Pressure
- Option 4: Freezing Point

2. **Define Colligative Properties**: Colligative properties depend on the number of solute particles in a solution. The main colligative properties include:
- Relative lowering of vapor pressure
- Depression of freezing point
- Elevation of boiling point
- Osmotic pressure

3. **Analyze Each Option**:
- **Boiling Point**: The boiling point can be affected by the presence of a solute, leading to boiling point elevation, which is a colligative property.
- **Vapor Pressure**: The vapor pressure of a solvent decreases when a solute is added, leading to relative lowering of vapor pressure, which is also a colligative property.
- **Osmotic Pressure**: Osmotic pressure is defined as the pressure required to stop the flow of solvent into a solution through a semipermeable membrane. It depends on the concentration of solute particles, making it a colligative property.
- **Freezing Point**: The freezing point of a solvent decreases when a solute is added, leading to freezing point depression, which is a colligative property.

4. **Conclusion**: All the options listed (boiling point elevation, vapor pressure lowering, osmotic pressure, and freezing point depression) are related to colligative properties. However, since the question asks for one option that is a colligative property, we can conclude that **Osmotic Pressure (Option 3)** is a colligative property.

### Final Answer:
**Osmotic Pressure (Option 3) is a colligative property.**