The carbon–carbon bond length is maximum in:

Correct answer: (c) CH₃CH₃

Explanation

A carbon–carbon bond gets shorter as more electron pairs are shared between the two carbons:

• ethane (CH₃CH₃), single bond: about 1.54 Å, the longest;
• benzene (C₆H₆), bonds between single and double because of resonance: about 1.39 Å;
• ethene (CH₂=CH₂), double bond: about 1.34 Å;
• ethyne (HC≡CH), triple bond: about 1.20 Å, the shortest.

So the C–C bond length is maximum in ethane.