Monomer Identification from Polymer Repeat Unit

Steps:

• Examine the repeat unit structure to identify the carbon chain and functional groups.
• Look for the linkage pattern, such as single bonds from an original double bond in addition polymerization.
• Match the repeat unit to the monomer by reversing the polymerization, adding a double bond where the chain connects.
• Compare with choices to find the exact structural match.

Why A is correct:

• The repeat unit matches the addition polymer of the alkene in A, where the double bond opens to form -CH2-CH(R)- linkages per the addition polymerization mechanism.

Why the others are wrong:

• B has a branched chain not present in the repeat unit.
• C includes an extra functional group like a carbonyl, absent in the unit.
• D features a cyclic structure, unlike the linear repeat unit.

Final answer: A