Correct option is (b) CH2=CH-Cl
To elaborate: Vinyl chloride (CH2=CH-Cl) is the monomeric unit of polyvinyl chloride. It is used for piping and cable insulation extensively. CF2=CF2, COOH-CH2-CH2-CH2–CH2COOH and C6H5-CH=CH2 are the monomers of Teflon, nylon, and polystyrene respectively.