The correct option is A a→q; b→r; c→p; d→s
(a) Bredig's arc method or electrodispersion method is used for the preparation of colloidal sol of gold, silver and platinum.
(b) In mechanical dispersion method, the substance is first ground to coarse particles and is used for preparation of graphite sol.
(c) The sound waves of high frequency are used in ultrasonic method and this method is used for preparation of sol of mercury, sulphides and oxides of metals.
(d) Peptisation is a process of converting a freshly prepared precipitate into colloidal form by the addition of a suitable electrolyte. KI and AgNO3 solutions are used for the peptisation of AgI precipitate.