Answer
(4) CH3CHCH2
Step-by-step explanation
Unsaturated hydrocarbons are hydrocarbons that have double or triple covalent bonds between adjacent carbon atoms.
So let us draw these structures quickly to see the one structure with a double or triple bond (unsaturated).
Only (4) CH3CHCH2 is the correct answer, (1) is NOT a hydrocarbon because it has chlorine.