No correct answer is (a)chain isomerism
this clearly shows that molecular formula of both is same but structure of carbon chain is different.
this can not be position isomer as you can see from iupac naming that their position of functional groups is same in both and how can it be functional isomer,in both the compounds functional group is same.

Functional isomerism is a type of isomerism in which compounds have the same molecular formula but different functional groups. In the given options, the compounds (CH3)3,CBr and CH3[CH2]3Br exhibit functional isomerism.

Explanation:
Functional isomerism occurs when compounds have the same molecular formula but differ in the arrangement of atoms, resulting in different functional groups.

(CH3)3,CBr and CH3[CH2]3Br both have the same molecular formula, C4H9Br. However, they have different functional groups.

(CH3)3,CBr:
- This compound is referred to as trimethylbromomethane.
- It consists of a central carbon atom (C) bonded to three methyl groups (CH3) and one bromine atom (Br).
- The functional group present in this compound is the alkyl group (CH3).

CH3[CH2]3Br:
- This compound is referred to as 1-bromobutane.
- It consists of a central carbon atom (C) bonded to a methyl group (CH3), a four-carbon chain (CH2)3, and one bromine atom (Br).
- The functional group present in this compound is the alkyl group (CH3).

Both compounds have the same molecular formula, C4H9Br, but they differ in the arrangement of atoms. (CH3)3,CBr has a branched structure with a tertiary carbon atom, while CH3[CH2]3Br has a linear structure with a primary carbon atom. This difference in structure leads to different functional groups, making them functional isomers.

To summarize, the compounds (CH3)3,CBr and CH3[CH2]3Br exhibit functional isomerism because they have the same molecular formula but different functional groups.