In oder that a hydrocarbon may undergo addtion reaction, it must be unsaturated in nature. It must be either an alkene (C=C) with general formula `C_(n)H_(2n)` or an alkyne `(C-=C)` with general formula `C_(n)H_(2n-2)`.
Out of the list of the hydrocarbons given:
* `C_(3)H_(6)` (Propene) is a alkene with C=C bond. it corresponds to general formula `C_(n)H_(2n)(n=3)`
* `C_(2)H_(2)` (Ethyne) is an alkyne with `C-=C` bond. it corresponds to general formula `C_(n)H_(2n-2)(n=2)`.
both these hydrocarbons take part in addition reaction. for example, they react with hydrogen upon heating to 473 K in the presence of Nickel catalyst to form corresponding alkanes.
`underset("Propane")(H-underset(H)underset(|)overset(H)overset(|)(C)-overset(H)overset(|)(C)=overset(H)overset(|)(C)=overset(H)overset(|)(C)-H)+H_(2)overset(Ni//473K)tounderset(("Propane"))(H-underset(H)underset(|)overset(H)overset(|)(C)-underset(H)underset(|)overset(H)overset()(C)-underset(H)underset(|)overset(H)overset(|)(C)-H)`
`underset("Ethyne")(H-C-=C-H+2H_(2))overset(Ni//473K)tounderset("Ethane")(H-underset(H)underset(|)overset(H)overset(|)(C)-underset(H)underset(|)overset(H)overset(|)(C)-H)`
