: Conditions for writing resonance structures: (1) The relative positions of the constituent atoms in all the structures should be the same. (2) All resonance structures should have the same, number of unpaired electrons. (3) All the resonance structures should have nearly the same energy. (4) In all resonance structures, like charges should not be placed on the adjacent atoms. In structure [c], N contains ten electrons in the valence shell which is not possible.