111.

Explain what is observed
(i) when a beam of light is passed through a colloidal sol.
(ii) an electrolyte, NaCl is added to hydrated ferric oxide sol.
(iii) electric current is passed through a colloidal sol?

(i) When a beam of light is passed through a colloidal solution, the path of light inside the colloidal solution is illuminated and becomes visible. The path of light inside a colloidal solution becomes visible because colloidal particles are big enough to scatter the light falling on them in all the directions. The scattering of light by colloidal particles is called Tyndall effect.

(ii) When NaCl is added to ferric oxide sol it dissociate to give Na⁺ and Cl^- ions. Particles of ferric oxide sol are positively charge.
thus they get coagulated in the presece of negatively charge Cl^- ion. 

(iii)The colloidal particles are charged and carry either positive or negtive charged particles in colloidal solution. When an electric curent is passed through a colloidal, solution, then depending on the nature of their charge, the colloidal particles move either towards the anode or towards the cathode, lose their charges and get deposited on the electrode. The migration of colloidal particles towards the oppositely charged electrodes under the influence of an electric field is called elecrophoresis.