Answer: The correct answer is: B Aeration.
A unit process where water and air are brought into intimate contact is known as aeration. The aeration of the flowing streams increases by turbulence and in industries during the process of aeration, the flow of water has opposite current to the air flow. The time of contact and the ratio of the air to water should be effective and sufficient to remove the unwanted gas and purify the air.
Aeration is used in decarbonation, stripping of ammonia and hydrogen sulphide, bacteria control etc.