Explain What is observed when:
(a) A beam of light is passed through a colloidal solution of As₂S₃
(b) An electrolyte (NaCl) is added to ferric hydroxide sol.
(c) An electric current is passed through a colloidal solution.

a) When beam of light passed through a colloidal solution of As₂S₃. the path of the light become visible beacuse of the tyndall effect.

b) When freshly precipitated Fe(OH)₃ is shaken with little amount of dilute solution of NaCl (electrolyte).
Peptization process  take place by converting the Fe(OH)₃ into colloidal solution.
As ferric hydroxide Fe(OH)₃ is positively charged sol it gets coagulated by Cl^- ion released by NaCl

c)The movement of colloidal particles under an applied electric potential is called electrophoresis. Positively charged particles move towards the cathode while negatively charged particles move towards the anode.