Mixtures of chlorinated derivatives of biphenyl, called polychlorinated biphenyls, or PCBs, were once prepared industrially on a large scale as insulating materials in electrical equipment. As equipment containing PCBs was discarded, the PCBs entered the environment at a rate that reached an estimated 25,000 lb/year. PCBs are very stable and accumulate in the fatty tissue of fish, birds, and mammals. They have been shown to be teratogenic, meaning that they induce mutations in the offspring of affected individuals. Some countries have banned the use of PCBs. A large number of chlorinated biphenyls are possible, and the commercially produced material is a mixture of many compounds.
(a) How many monochloro derivatives of biphenyl are possible?
(b) How many dichloro derivatives are possible?
(c) How many octachloro derivatives are possible?
(d) How many nonachloro derivatives are possible?