Correct answer is (b) Thioether oxidation
For explanation I would say: Thioether oxidation, usually performed by microbial population by oxidizing the Sulphur present in the pesticides. Heavy metals are not pesticides and they definitely can affect the microbial population in the habitat as they have the potential to degrade the organisms present in the environment. Green algae and oxygen are the compounds that are not harmful to the microbial population or the environment and it not a process that would help in degradation of pesticides using microbial population.