Tautomerism is not exhibited by

Benzoquinone does not exhibit tautomerism.

The presence of$\alpha$ -hydrogen on a saturated carbon attached to C = O, NO, ${\mathrm{NO}}_2$, etc. or should have an H-atom present on a heteroatom (O, N, S, etc.) coupled to a double bond is a necessary requirement for tautomerism. Option (a) does not display tautomerism because it lacks$\alpha$ -hydrogen on a saturated carbon.