Which of the following are functional isomers of?
Let us look at the definition of a functional isomer.
Functional isomers are constitutional isomers bearing different functional groups. As in, you have to look for compounds having the same molecular formula but different structural arrangements such that they have distinctly different functional groups. For instance, CH3CH2CHO - Propanal and CH3COCH3 - Propanone.
The compound shown above is the is the tautomer of O-Cresol. In general, tautomers are not considered as functional isomers.
The given compound is an aromatic alcohol.
is an aromatic ether also known as Anisole.