Question

The number of compounds which can undergo tautomerism are :

Answer 1

For (a) Nitroso-oxime tautomerism is shown as follows :

Here Nitroso form is more stable due to aromaticity.
For (b) and (d) :


In (b) keto form is more stable because there is no stabilizing factor in enol form .
In (d) the enol form is highly stable because it is aromatic in nature
In compound (c) there are no $s{p}^3$ hybridised carbon having $\alpha$-hydrogens, so no tautomerism is observed in this case

So the correct answer is 3