An alkene is a hydrocarbon that contains a carbon-carbon double bond, whereas an alkane is a hydrocarbon that contains only single bonds between the carbon atoms. The process that converts an alkene to an alkane is called hydrogenation, which involves the addition of hydrogen gas (H2) across the carbon-carbon double bond. In this reaction, the double bond is broken, and the two carbon atoms are each bonded to a hydrogen atom, forming a single bond. This reaction is commonly carried out in the presence of a metal catalyst, such as platinum, palladium, or nickel, which speeds up the reaction by facilitating the adsorption of hydrogen molecules onto the surface of the metal. Therefore, the correct answer is hydrogenation.