Which one of the following does not involve coagulation?
(4) (1) Blood is a colloidal sol and is coagulated by FeCl3.
(2) When two rivers meet, they also carry colloidal sols of opposite charge. There is coagulation.
(3) Potash alum causes coagulation of impurities.
(4) Peptisation is reverse of coagulation and is observed when a common ion is adsorbed on the precipitate.