High Quality Content by WIKIPEDIA articles! Polychlorinated biphenyls (PCBs; CAS number 1336-36-3 ) are a class of organic compounds (specifically organochlorides) with 2 to 10 chlorine atoms attached to biphenyl, which is a molecule composed of two benzene rings. The chemical formula for PCBs is C12H10-xClx. There are 209 different variable of these arrangements and orientations that make up the PCB family, but only 130 are commercially used.