Nylon's polyamide repeating unit

Steps:

• Recall nylon is a synthetic polyamide polymer formed by condensation polymerization of diamines and dicarboxylic acids.
• Identify the key structural feature: repeating units with amide (-CONH-) linkages connecting hydrocarbon chains.
• Compare choices to standard nylon 6,6 structure: -[NH-(CH2)6-NH-CO-(CH2)4-CO]-.
• Select the option matching this amide-based partial chain.

Why C is correct:

• It depicts the characteristic amide bond (-CONH-) in a linear chain, matching the definition of polyamides like nylon.

Why the others are wrong:

• A shows ester linkages (-COO-), typical of polyesters, not nylons.
• B lacks amide groups, resembling polyethylene or alkane chains.
• D features branched or aromatic structures, unlike nylon's aliphatic backbone.

Not enough information on exact choice visuals, but based on standard representations, C fits.

Final answer: C