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 determine which phenomenon exhibits the Tyndall effect, we need to first understand what the Tyndall effect is.

### Step-by-Step Solution:

1. **Understanding the Tyndall Effect**:
- The Tyndall effect is the scattering of light by colloidal particles. When light passes through a colloidal solution, the particles scatter the light, making the path of the light beam visible.

2. **Analyzing the Options**:
- **Option 1: Blue color of the sky**:
- The blue color of the sky is due to Rayleigh scattering, which occurs when light is scattered by particles that are much smaller than the wavelength of light. This is not the Tyndall effect.
- **Option 2: Twinkling of stars**:
- The twinkling of stars is caused by atmospheric refraction of starlight as it passes through varying layers of the Earth's atmosphere. This phenomenon is also not related to the Tyndall effect.
- **Option 3: Tail of a comet**:
- The tail of a comet consists of tiny particles and ionized gas. As the comet approaches the sun, it releases dust and gas, which can scatter light. The scattering of light by these tiny solid particles in the comet's tail is an example of the Tyndall effect.
- **Option 4: None of the above**:
- Since we have identified that the tail of a comet exhibits the Tyndall effect, this option is incorrect.

3. **Conclusion**:
- Based on the analysis, the correct answer is **Option 3: Tail of comet**, as it is the phenomenon that exhibits the Tyndall effect.

### Final Answer:
The phenomenon exhibiting the Tyndall effect is the **Tail of a comet**.