Question

Alum helps in purifying water by
(a) forming Si complex with clay particles
(b) sulphate part which combines with the dirt and removes it
(c) coagulating the mud particles
(d) making mud water soluble.

Answer 1

(c) : The negatively charged colloidal particles of impurities get neutralised by the Al³⁺ ions and settle down and pure water can be decanted off.