Tyndall effect is observed when:

Options

A. The diameter of dispersed particles is much smaller than the wavelength of light used.
B. The diameter of dispersed particles is much larger than the wavelength of light used.
C. The refractive index of dispersed phase is greater than that of the dispersion medium.
D. The diameter of dispersed particles is similar to the wavelenght of light used.

Explanation

To determine when the Tyndall effect is observed, we need to analyze the conditions required for this phenomenon. The Tyndall effect occurs when light is scattered by particles in a colloid or in very fine suspensions. Here’s a step-by-step solution:

### Step-by-Step Solution:

1. **Understanding the Tyndall Effect**:
- The Tyndall effect is the scattering of light by particles in a colloid or very fine suspension. This scattering causes the light to become visible as it passes through the medium.

2. **Identifying the Key Conditions**:
- For the Tyndall effect to be observed, certain conditions must be met regarding the size of the particles and the wavelength of light:
- The diameter of the dispersed phase particles should be comparable to the wavelength of the light used.
- The refractive indices of the dispersed phase and the dispersing medium should be significantly different.

3. **Analyzing the Options**:
- **Option A**: States that the diameter of the dispersed phase particle is much smaller than the wavelength of light. This is incorrect because we need the sizes to be comparable.
- **Option B**: Indicates that the diameter of the dispersed particle is not much smaller than the wavelength of light used. This is a correct condition.
- **Option C**: Suggests that the refractive indices of the dispersed phase and the dispersed medium should be almost similar. This is incorrect as there should be a significant difference.
- **Option D**: Similar to C, it suggests that the refractive indices should be similar, which is also incorrect.

4. **Conclusion**:
- Based on the analysis, the correct conditions for observing the Tyndall effect are met in Option B. Therefore, the Tyndall effect is observed when the diameter of the dispersed phase particles is not much smaller than the wavelength of light, and there is a significant difference in the refractive indices of the dispersed phase and the medium.

### Final Answer:
The Tyndall effect is observed when the diameter of the dispersed phase particles is comparable to the wavelength of light and the refractive indices of the dispersed phase and the medium are significantly different.

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