Monomer Identification in Addition Polymers

Steps:

• Examine the polymer structure: Polystyrene's repeating unit is -[CH₂-CH(C₆H₅)]-, with a phenyl group on every second carbon.
• Recall addition polymerization: The monomer's carbon-carbon double bond breaks to form single bonds linking units.
• Derive monomer: Remove the bond between repeating units to restore the double bond, yielding CH₂=CH(C₆H₅).
• Match to choices: This structure is styrene, corresponding to option B.

Why B is correct:

• Styrene (C₆H₅CH=CH₂) is the defined monomer for polystyrene, where the vinyl group (-CH=CH₂) adds to form the chain per addition polymerization rules.

Why the others are wrong:

• A: Lacks phenyl group, resembling ethene, which forms polyethylene.
• C: Contains extra functional groups, not matching the simple alkene structure.
• D: Incorrect double bond position or substituent, altering the repeating unit.

Final answer: B