A and b are tautomers of each other
I know that, I want to know why they are not resonating structures
For resonance, the basic structure of compound must be same .
But , here in fig 1 H is attached with N
And in fig 2 H is attached with O
So basic structure is different and hence they can’t be resonance structures
Resonance is the distribution of pi electrons through a conjugated system, only electrons. So, any nucleus shift is not allowed.