A phenomenon exhibiting Tyndall effect is:

Options

A. Blue colour of sky
B. Twinkling of stars
C. Tail of comets
D. All of these

Answer

To solve the question "A phenomenon exhibiting Tyndall effect is:", we need to understand what the Tyndall effect is and identify examples of phenomena that exhibit this effect.

### Step-by-Step Solution:

1. **Understanding the Tyndall Effect**:
- The Tyndall effect is the scattering of light by particles in a colloid or in very fine suspensions. When a beam of light passes through such a medium, the light is scattered, making the path of the beam visible.

2. **Conditions for the Tyndall Effect**:
- For the Tyndall effect to occur, the size of the particles must be comparable to the wavelength of the light. The wavelength of visible light ranges from approximately 400 nm to 700 nm, while colloidal particles typically range from 1 nm to 1000 nm.

3. **Examples of the Tyndall Effect**:
- Common examples of phenomena that exhibit the Tyndall effect include:
- **Colloidal solutions**: Such as milk or fog, where the particles are large enough to scatter light.
- **Dust in the air**: When sunlight passes through a dusty room, the dust particles scatter the light, making the beam visible.
- **Smoke**: Similar to dust, smoke particles can scatter light, showing the path of the beam.

4. **Conclusion**:
- Based on the understanding of the Tyndall effect and the examples provided, we can conclude that a phenomenon exhibiting the Tyndall effect is a colloidal solution, such as milk or fog.

### Final Answer:
A phenomenon exhibiting the Tyndall effect is a colloidal solution, such as milk or fog.