The correct answer is Addition reaction. Key Points - Unsaturated hydrocarbons add hydrogen in the presence of catalysts such as palladium or nickel to give saturated hydrocarbons. - Catalysts are substances that cause a reaction to occur or proceed at a different rate without the reaction itself being affected. - This reaction is an example of Addition reaction which is commonly used in the hydrogenation of vegetable oils using a nickel catalyst. - Vegetable oils generally have long unsaturated carbon chains while animal fats have saturated carbon chains.