Question

Name the resonance effect exhibited in nitrobenzene

Answer 1

We never really need to know the number of resonance structures. The whole concept is qualitative, so we can't draw any quantitative conclusions from it. But if you want to do it anyway, then of course 1 and 5 are the same, while 2 and 4 are not (they have positive charges on different atoms).

Also, both oxygens are in fact equivalent, so you might want to add the structures with their roles reversed.

Answer 2

I was studying about the resonance and here's my doubt: How many resonating structures are there in nitrobenzene? Is it 5 (as drawn) or is it 4