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 tiny particles (colloids) dispersed in a continuous medium (liquid or gas). The size of these particles typically ranges from 1 nm to 1000 nm (1 mm).

2. **Observation Under a Microscope**:
- When observing a colloidal sol under a microscope, we are interested in the behavior of these particles when illuminated by light.

3. **Light Scattering**:
- The particles in a colloidal sol are large enough to scatter light. This scattering occurs because the size of the colloidal particles is comparable to the wavelength of visible light (400 nm to 750 nm).

4. **Visible Light and Particle Size**:
- Since the size of colloidal particles is between 1 nm and 1000 nm, they can effectively scatter visible light. This scattering makes the path of light visible when viewed through a microscope.

5. **What We Can See**:
- Under the microscope, we cannot see the individual particles directly. Instead, we observe the scattered light, which gives us an indication of the presence of these particles. This phenomenon is known as the Tyndall effect.

6. **Conclusion**:
- Therefore, when a colloidal sol is observed under a microscope, we can see the scattering of light rather than the particles themselves.