In which of the following species are all carbon-carbon bond lengths equal?

Step-by-step solution

The species in option (B) is the squarate dianion ( C₄O₄²⁻ ). It is a highly symmetric system that exhibits extensive resonance. Due to this resonance, the negative charges are equally delocalized over all four oxygen atoms, and the electrons are delocalized over the entire carbon ring. This perfect delocalization results in all four carbon-carbon bonds having the same partial double bond character, making all carbon-carbon bond lengths equal. In option (A), the unsymmetrical substitution by the -NO₂ group breaks t