Chemistry - STRUCTURAL ISOMERISM Question with Solution | TestHub

(III) is 2-phenylpropanal, CH₃-CH(Ph)-CHO, and (IV) is its enol, CH₃-C(Ph)=CH-OH : they differ only in the position of a proton and a double bond, so they are tautomers. (II) and (III) are the same aldehyde drawn in two ways (identical, not geometrical isomers); (I) and (II) are tautomers of each other, not metamers; (I) and (IV) are the same enol (geometrical/E-Z pair at most), not tautomers. Hence (C).