Correct Option
The correct option is (c).
Explanation
The Tyndall effect is the phenomenon of scattering of a beam of light by medium-sized particles suspended in a colloid. This scattering makes the path of the light beam visible within the mixture. The visibility of the path depends on the size of the particles relative to the wavelength of light.
Statement-wise Analysis
- Statement 1 is Incorrect: A solution of copper sulphate is a true solution (homogeneous mixture). In true solutions, the solute particles are extremely small (less than 1 nm in diameter). These particles are too small to scatter a beam of light. Therefore, the Tyndall effect is not observed.
- Statement 2 is Correct: A mixture of water and milk is a colloid (heterogeneous mixture). The particles in a colloid are larger than those in a true solution but smaller than those in a suspension. These particles are large enough to scatter a beam of light passing through it, exhibiting the Tyndall effect.
- Statement 3 is Correct: The fundamental definition of the Tyndall effect involves the scattering of light by particles, which results in the path of the light becoming visible to an observer. Without scattering, the light beam would pass through the medium invisibly (as seen in true solutions).
Key Takeaway
True solutions do not show the Tyndall effect because their particles are too small to scatter light. Colloids show the Tyndall effect because their particles are large enough to scatter light, making the beam's path visible.