Monomer identification from polymer repeating unit

Steps:

• Examine the polymer W section to identify the repeating unit, which shows -[CHCl₂-CCl(CH₃)]- linkage from addition polymerization.
• Match the unit to a monomer with a double bond that opens to form this chain: Cl₂C=CCl-CH₃.
• Confirm the monomer's name based on carbon chain (three carbons) and chlorine positions (two at C1, one at C2).
• Eliminate options with mismatched carbon count or substituent positions.

Why C is correct:

• 1,1,2-Trichloropropene (Cl₂C=CCl-CH₃) adds across the double bond to yield the exact repeating unit -[CHCl₂-CCl(CH₃)]-, per standard alkene polymerization rules.

Why the others are wrong:

• A: 1,1,2-Trichlorobutene has four carbons, producing a longer repeating unit not matching the polymer.
• B: 1,2-Dichlorobutene lacks the geminal dichloride and has only two chlorines, yielding -[CHCl-CHCl-CH₂-CH₃]- unit.
• D: 1,2-Dichloro-2-methylethene is C₃H₄Cl₂ with incorrect chlorine placement, forming -[CHCl-CCl(CH₃)]- without the CHCl₂ group.

Final answer: C