TFTF
FTTF
TTFT
TFFT
Functional group -
Atom or group of atom on which almost all chemical properties depend is called functional group.
- wherein
Functional group isomerism. Functional isomers are structural isomers that have the same molecular formula (that is, the same number of atoms of the same elements), but the atoms are connected in different ways so that the groupings are dissimilar. Dimethyl ether and ethanol are functional isomers.
Metamerism is a type of structural isomerism in which different alkyl groups are attached to the same functional group.
Therefore, Option(3) is correct.