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.