Polymer Structure from Symmetric Alkene Monomer

Steps:

• Identify polymer G structure: repeating -CH(CH3)-CH(CH3)- units, where each chain carbon bonds to one H and one CH3.
• Recall addition polymerization: alkene double bond breaks, linking carbons while preserving substituents.
• Examine monomer options: match symmetric alkene with CH3 on each =C carbon.
• Confirm but-2-ene (CH3-CH=CH-CH3) yields -[CH(CH3)-CH(CH3)]_n- matching description.

Why B is correct:

• But-2-ene's formula CH3-CH=CH-CH3 polymerizes to -[CH(CH3)-CH(CH3)]_n-, placing one H and one CH3 on every chain carbon per addition polymerization mechanism.

Why the others are wrong:

• A. But-1-ene (CH2=CH-CH2CH3) gives alternating CH2 (two H) and CH(CH2CH3) (one H, one ethyl) carbons.
• C. Methylpropene ((CH3)2C=CH2) yields CH2 (two H) and C(CH3)2 (no H, two CH3) carbons.
• D. Propene (CH3-CH=CH2) produces CH2 (two H) and CH(CH3) (one H, one CH3) alternating carbons.

Final answer: B