The cotterells precipitator is used to :
(a) neutralize charge on carbon particles in air in smoke
(b) coagulate carbon atoms of smoke
(c) bring in cataphoresis in carbon particles
(d) all of the above
(d) The negatively charged carbon particles in air (smoke) are moved towards anode due to cataphoresis, where they are neutralized to left free air. The process is used to control air pollution.
Foam is a colloidal solution of:
(a) gaseous particles dispersed in gas (c) solid particles dispersed in a liquid
(b) gaseous particles dispersed in a liquid (d) solid particles dispersed in gas
(b) Foam is a colloidal state of gas dispersed in liquid (froths) or in solid, i.e., solid foam (mattresses).
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) aluminium which coagulates the mud particles
(d) making mud water soluble
(c) Al3+ is very good coagulating agent for -ve sol (muddy water).