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Tautomers are structural isomers where interconversion in an acidic or a basic medium takes place. The process of conversion of one tautomer into another is known as tautomerization.One example is keto-enol tautomers.

The difference in the bonding pattern for keto-enol tautomers lies in the position of a double bond and a proton. A keto has a C=O and an additional C-H bond, while an enol has a C-OH and a C=C bond.They are constitutional isomers and lie in equilibrium with each other.

Generally, keto is considered to be more stable due to the stronger C=O present.

Based on the explanations, the enol tautomer(s) for each compound is shown below:

Keto-enol form of a.

Keto-enol form of b.

Keto-enol form of c,