Saturated hydrocarbons. (alkanes) general formula - C(n) H2(n)+2 where n = no. of carbon atoms. The essential condition is that the compound should be unsaturated. i.e. it should contain a double or triple bond. Catalysts are also needed for the reaction to take place.
C2H4 + H2 --(nickel/palladium catalyst)---> C2H6