In which of the following molecules does the mesomeric effect NOT operate?

Step-by-step solution

The mesomeric effect (or resonance effect) operates when there is conjugation between a substituent and the system of the ring. This requires the substituent to have either a lone pair of electrons (for +M effect) or a bond/vacant p-orbital (for -M effect) adjacent to the conjugated system. In option (A), the -N⁺ N group has a bond in conjugation with the benzene ring. It acts as a strong electron-withdrawing group via the -M effect. In option (B), the -N⁺(CH₃)₃ group has a nitrogen atom bonded to four carbon atoms