Chemistry - STRUCTURAL ISOMERISM Question with Solution | TestHub

Compound (C) undergoes oxime-nitroso tautomerism, where the hydrogen from the $=N-OH$ group migrates to the carbonyl oxygen, converting the quinonoid structure into a stable aromatic p-nitrosophenol form.

Compound (D) is an enol form of a $\beta$-diketone, which exists in a dynamic keto-enol tautomeric equilibrium with its corresponding dicarbonyl form.

Compounds (A) and (B) cannot show tautomerism because they completely lack the necessary acidic $\alpha$-hydrogens (or active conjugated hydrogens) to participate in the proton shift.