Bisphenol A (BPA), a cause of concern, is a structural/key component in the manufacture of which of the following kinds of plastics? ​

The correct answer is B) Polycarbonate. Bisphenol A is one of the two main monomers used to make polycarbonate, the other being phosgene (or diphenyl carbonate in newer routes). The two react by condensation polymerisation, releasing small molecules, and the result is a tough, transparent plastic used in water bottles, CDs and similar products. BPA is also used in epoxy resins, which is why it is a food-contact concern.

• A) Low-density polyethylene: Made by addition polymerisation of ethylene. No bisphenol is involved.
• C) Polyethylene terephthalate: Made from terephthalic acid (or dimethyl terephthalate) and ethylene glycol. BPA is not a monomer here.
• D) Polyvinyl chloride: Made from vinyl chloride. Its concern is phthalate plasticisers, not BPA.

The concept is the difference between addition and condensation polymers. For Mains, BPA links to endocrine-disrupting chemicals, food safety regulation, and the debate on plastic waste and health. Many countries now restrict BPA in baby feeding products, and 'BPA-free' labelling has become common.

Trap: Aspirants often pick PVC or PET because they associate them with 'harmful plastics' or bottles. Remember that the question asks about the monomer, and BPA belongs to polycarbonate and epoxy resins.