Which of the following shows the Tyndall effect?(i) common salt(ii) milk(iii) copper sulphate solution(iv) starch solution

The Tyndall effect is the scattering of light as a light beam passes through a colloid. The individual suspension particles scatter and reflect light, making the beam visible. The Tyndall effect is particularly applicable to colloidal mixtures and suspensions; it does not occur in true solutions.

(i) Common salt (sodium chloride) in water forms a true solution and does not show the Tyndall effect.

(ii) Milk is a colloidal mixture because it consists of tiny particles of fat dispersed in water. The particles are large enough to scatter light, making milk an example of a mixture that shows the Tyndall effect.

(iii) Copper sulphate solution is a true solution and does not show the Tyndall effect.

(iv) Starch solution is a colloidal solution because it consists of large molecules dispersed in water. These molecules are large enough to scatter light, making a starch solution another example of a mixture that shows the Tyndall effect.

So, the mixtures that show the Tyndall effect are milk and starch solution.