Tyndall effect is observed only when
(i) the diameter of the dispersed particles is not much smaller than the wavelength of the light used.
(ii) the refractive indices of dispersed phase and dispersion medium differ greatly in magnitude .
(iii) the size of the particles is generally between `10^(-11) and 10^(-9)` m in diameter.
(iv) the dispersed phase and dispersion medium cna be seen separately in the system .

Options

A. (i) and (iii)
B. (i) and (iv)
C. (ii) and (iii)
D. (i) and (ii)

Answer

To determine when the Tyndall effect is observed, we will analyze each option provided in the question step by step.

### Step 1: Understanding the Tyndall Effect
The Tyndall effect is the scattering of light by particles in a colloid or particles in a very fine suspension. It is most commonly observed when light passes through a colloidal solution.

### Step 2: Analyzing the Options
1. **Option (i)**: The diameter of the dispersed particles is not much smaller than the wavelength of the light used.
- **Analysis**: This statement is true. For the Tyndall effect to be observed, the size of the dispersed particles should be comparable to the wavelength of light (around 400-700 nm for visible light). If the particles are much smaller than the wavelength, they will not scatter light effectively, and the Tyndall effect will not be observed.

2. **Option (ii)**: The refractive indices of dispersed phase and dispersion medium differ greatly in magnitude.
- **Analysis**: This statement is also true. A significant difference in refractive indices between the dispersed phase and the dispersion medium is necessary for light scattering to occur, which is essential for the Tyndall effect.

3. **Option (iii)**: The size of the particles is generally between \(10^{-11}\) and \(10^{-9}\) m in diameter.
- **Analysis**: This statement is false. Particles in this size range are typically considered to be in the range of true solutions rather than colloids. The Tyndall effect is not observed in true solutions.

4. **Option (iv)**: The dispersed phase and dispersion medium can be seen separately in the system.
- **Analysis**: This statement is false. If the dispersed phase and the dispersion medium can be seen separately, it indicates that they are not mixed properly, and thus a colloidal solution (where the Tyndall effect is observed) is not formed.

### Conclusion
Based on the analysis:
- **Correct Options**: (i) and (ii)
- **Incorrect Options**: (iii) and (iv)

### Final Answer
The Tyndall effect is observed only when options (i) and (ii) are true.

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