(i) Scattering of light by the colloidal particles takes place and the path of Iight becomes illuminated. This is called Tyndall effect.
(ii) The positively charged colloidal particles of hydrated ferric oxide sol get coagulated by the oppositely charged ions provided by electrolyte NaCl.
(iii) On passing direct current, the colloidal particles move towards the oppositely charged electrode where they lose their charge and get coagulated.