Polymer structures from monomer types Steps:

• Identify X as addition polymer of but-1-ene (CH₂=CHCH₂CH₃); double bond opens to form repeat unit -CH₂CH(CH₂CH₃)-, often notated linearly as [CH₂CH₂CH(CH₃)CH₂].
• Confirm Y as condensation polymer from diol (HOCH₂CH₂OH) and dicarboxylic acid (HOOCCH₂COOH), linking via ester bonds.
• Match options: [CH₂CH(CH₃)] is propene unit (C₃H₆); [CH₂CH₂CH(CH₃)CH₂] fits but-1-ene (C₄H₈) with ethyl branch.
• Select option with correct X unit and Y as polyester (not polyamide, which requires diamine).

Why C is correct:

• But-1-ene's addition polymerization gives -[CH₂CH₂CH(CH₃)CH₂]- repeat unit per standard notation, and Y forms polyester via condensation of diol and diacid (ester linkage: -COO-).

Why the others are wrong:

• A: X repeat unit [CH₂CH(CH₃)] matches propene, not but-1-ene.
• B: X repeat unit wrong; Y is polyester, not polyamide.
• D: Y is polyester from diol/diacid, not polyamide.

Final answer: C