Answer:
D: CnH2n
Explanation:
Unsaturated hydrocarbons have double and/or triple bonds between carbon atoms. Those with double bond assuming they have non-cyclic structures are called alkenes with the general formula C_nH_2n. Meanwhile the hydrocarbons that possess triple bonds are called alkynes and possess the general formula CnH2n-2.
Looking at the options, for alkenes, the correct answer is option D