The correct option is
B unsaturated aliphatic hydrocarbons
Alkenes and alkynes are unsaturated aliphatic hydrocarbons as they contain carbon carbon multiple bonds and contain only two elements C and H.
For example, propene CH3−CH=CH2 (Alkene) and propyne CH3−C≡CH (Alkyne) are unsaturated hydrocarbons.
Hence option B is correct.