The correct answer is A. Increases.
Chlorination is a process of disinfecting water by adding chlorine to it. Chlorine kills bacteria by attacking their cell membranes, which causes them to rupture and die. The higher the temperature of the water, the more effective chlorine is at killing bacteria. This is because heat increases the rate of chemical reactions, including the reaction between chlorine and bacteria.
Option B is incorrect because the death rate of bacteria increases with the rise in temperature of water. Option C is incorrect because the death rate of bacteria does not remain unaffected with the rise in temperature of water. Option D is incorrect because the correct answer is A.