The correct option is C Functional isomers
Propanone (a ketone) and,
Prop-2-en-1-ol (a alcohol) with molecular formula C5H10O exhibit functional isomerism.
Functional isomerism, an example of structural isomerism, occurs when substances have the same molecular formula but different functional groups. This means that functional isomers belong to different homologous series.
Hence, Option a is correct.