What is the repeating unit of PVC?

• A. -CH2-CH2-
• B. -CH2-CHCl-
• C. -CH2-CHBr-
• D. -CHCl-CH2-

Answer: (B)

The key idea is that a polymer’s repeating unit comes from the monomer’s skeleton after polymerization, including the substituents that stay with the chain. PVC is made from vinyl chloride, CH2=CHCl. When the double bond opens, the two carbons become part of a long chain, and the chlorine on one of those carbons remains attached to every second carbon along the chain. That gives the repeating unit -CH2-CHCl-.

So the polymer is a chain of -CH2-CHCl- units. The other options would either lack chlorine entirely (polyethylene), have a different halogen (bromine instead of chlorine), or place the chlorine on the other carbon of the unit (which is just a different way to write the same unit, but the conventional way to show PVC is -CH2-CHCl-).