JEE Main · 2021 · 25 Jul 2021 · Shift 1 · General Organic Chemistry

Resonance structures of one species must keep every nucleus where it is and may not put charges of the same sign on two bonded atoms, because that electrostatic penalty is not repaid by any delocalisation. Three of the drawings only move $\pi$ electrons of the carbon chain and of the nitro group, leaving the positive charge on nitrogen and the negative charge on oxygen or on a carbon well away from it. The remaining one places a carbocation on the very carbon that is bonded to the positively charged nitrogen of the nitro group, so two positive centres sit on adjacent bonded atoms, and it sets a carbanion directly beside that carbocation instead of writing the pair as a $\pi$ bond. The structure with a positively charged carbon attached to the nitro nitrogen is not a correct resonance form.