The hydrocarbon having molecular mass of 70 is `C_5H_10`. It exists in the following four structural isomers : (i)`CH_3CH_2CH_2CH=CH_2` (pent-1-ene), (ii)`(CH_3)_2CH-CH=CH_2` (3-methylbut-1-ene) , (iii)`CH_3CH_2CH=CHCH_3` (pent-2-ene) and (iv)`(CH_3)_2C=CHCH_3` (2-methylbut-2-ene)]