The full form of PCB, an air pollutant, is

PCB stands for polychlorinated biphenyl, a persistent chlorinated pollutant.

Polychlorinated benzene wrongly names benzene in place of biphenyl.

Perchloro biphenyl misstates the chlorination as perchloro rather than poly.

Perchloro benzene errs on both the compound and the chlorination term.

PCBs were once used in transformers, coolants and lubricants.

Their toxicity and persistence led to a worldwide ban.