A colligative property out of the following is :

Options

A. change in free energy
B. change in pressure
C. heat of vapourization
D. osmotic pressure.

Answer

To determine which of the following is a colligative property, we need to understand what colligative properties are. Colligative properties are those 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.

### Given Options:
1. Change in free energy
2. Change in pressure
3. Heat of vaporization
4. Osmotic pressure

### Step-by-Step Solution:

**Step 1: Define Colligative Properties**
- Colligative properties depend on the number of solute particles in a solution. Common examples include vapor pressure lowering, boiling point elevation, freezing point depression, and osmotic pressure.

**Step 2: Analyze Each Option**
- **Change in Free Energy**: This property is related to the thermodynamic state of a system and does not depend on the number of solute particles. Therefore, it is **not a colligative property**.

- **Change in Pressure**: This is a general term and does not specifically relate to the number of solute particles in a solution. Thus, it is **not a colligative property**.

- **Heat of Vaporization**: This is a thermodynamic property that describes the energy required to convert a liquid into a gas. It does not depend on the number of solute particles, so it is **not a colligative property**.

- **Osmotic Pressure**: This is defined as the pressure required to prevent the flow of solvent into a solution via osmosis. Osmotic pressure is directly proportional to the concentration of solute particles in the solution, which makes it a **colligative property**.

**Step 3: Conclusion**
Based on the analysis, the only option that qualifies as a colligative property is **osmotic pressure**.

### Final Answer:
**Osmotic pressure is a colligative property.**

---