Correct Answer - B
Structures (1) and (3) are the kekule resonance structures. The resonance hybrid has only one C- to -C bond length and bond energy. This length is intermediate between that of a single and double bond. The hypothetical cyclohexatriene or would have two different alternating C-C and `C=C` bond length with different bond energies The hybrid is more stable and hence less reactive than the hypothetical cyclohexatriene.
