Which of the following compound is not an unsaturated hydrocarbon?

The molecule is referred to as being unsaturated if the carbon contains one (or) more double (or) triple bonds in the carbon atoms.  Arenes, Alkenes and Alkynes contain at least one double bond. Hence they are unsaturated.

 In comparison to saturated carbon molecules, unsaturated carbon compounds are more reactive. 

Propene, benzene, and butyne are examples of unsaturated hydrocarbons.

Alkanes are saturated compounds because they do not have double or triple bonds. These compounds have single bonds.