Copolymer Structure Reveals Second Monomer

Steps:

• Analyze the polymer diagram for repeating units from two monomers.
• Confirm propene unit as -CH₂-CH(CH₃)- from CH₃CH=CH₂.
• Identify adjacent unit as -CH₂-CH₂-, indicating ethene (CH₂=CH₂) as the other monomer.
• Compare to choices; D matches ethene structure.

Why D is correct:

• Ethene (CH₂=CH₂) undergoes addition polymerization to form -CH₂-CH₂- units, directly matching the diagram's copolymer linkage with propene.

Why the others are wrong:

• A: Shows ethane (CH₃CH₃), a saturated alkane unable to form addition polymers.
• B: Depicts propene again, but the polymer uses two different monomers.
• C: Represents a branched alkene like butene, yielding mismatched -CH₂-CH(C₂H₅)- units.

Final answer: D