When a colloidal sol is observed under a microscope we can see,

Options

A. Light scattered by colloidal particles
B. Size of colloidal particles
C. Shape of colloidal particles
D. Relative size of the colloidal particles

Answer

### Step-by-Step Solution:

1. **Understanding Colloidal Sols**:
- A colloidal sol consists of particles that are dispersed in a medium. The size of colloidal particles ranges from 1 nanometer to 1000 nanometers.

2. **Observation Under a Microscope**:
- When we observe a colloidal sol under a microscope, we cannot see the individual colloidal particles directly due to their small size.

3. **Scattering of Light**:
- Colloidal particles have the ability to scatter light. This phenomenon is known as the Tyndall effect. When light passes through a colloidal solution, it interacts with the colloidal particles, causing the light to scatter.

4. **What We Can See**:
- Under the microscope, we can observe the scattering of light caused by the colloidal particles. This scattering indicates the presence of colloidal particles in the solution.

5. **Conclusion**:
- Therefore, when a colloidal sol is observed under a microscope, we can see the light scattering effect (Tyndall effect) caused by the colloidal particles.