Which of the following is not a colligative property ?

Options

A. Osmotic pressure
B. Depression in freezing point
C. Lowering of vapour pressure
D. Depression in boiling point

Answer

To determine which of the following 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, rather than the identity of the solute itself. The four main colligative properties are:

1. **Relative lowering of vapor pressure**
2. **Elevation of boiling point**
3. **Depression of freezing point**
4. **Osmotic pressure**

Now, let's analyze each option provided in the question (assuming typical options like boiling point elevation, freezing point depression, vapor pressure lowering, and something that is not a colligative property):

1. **Relative lowering of vapor pressure**: This is a colligative property because it depends on the number of solute particles in the solution.

2. **Elevation of boiling point**: This is also a colligative property, as it is influenced by the number of solute particles.

3. **Depression of freezing point**: This is another colligative property, which again depends on the number of solute particles.

4. **Osmotic pressure**: This is also a colligative property, as it is determined by the concentration of solute particles in a solution.

If we consider an option that is not a colligative property, it could be something like "pH of the solution" or "color of the solution." These properties do not depend on the number of solute particles but rather on the nature of the solute.

Thus, the answer to the question is that any property that does not depend on the number of solute particles is not a colligative property.

### Final Answer:
The property that is not a colligative property is **pH of the solution** (or any other similar property that does not depend on the number of solute particles).