Correct option is: (A) chain isomerism
The molecules which have same molecular formula but they differ in the branching of chain. Hex-2-one and 2-methylpent-2-ene have same molecular formula \((C_6H_{12})\) but they differ only in the branching of chain. Therefore, Hex-2-ene and 2-Methylpent-2-ene are chain isomers
