Given, Which of the given compounds can exhibit tautomerism? NEET 2015 (Phase 1)

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All compounds show tautomerism.

Of many types of tauomerism possible, keto-enol tauomerism is the most commonly encountered one.

It is possible in presence of $α$ -C (wrt the carbonyl group), which is the conjugate C-H bond having sp³ hybridization.

Usually it is the $α$ -C of the carbonyl group constituting a triad system, however it could also sometimes be the $γ$ -C, if there is a C=C present on $α - β$ carbons, constituting a quinquad system.

Compound (I) & (II) are have tautomerism in a triad system, while (III) involves a quinquad system as shown here:

Chemistry - STRUCTURAL ISOMERISM Question with Solution | TestHub

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