Which of the following can be used as a catalyst in Hydrogenation reaction?

Palladium

The correct answer is option 4. Palladium.

Palladium is commonly used as a catalyst in hydrogenation reactions. Hydrogenation is a chemical reaction in which hydrogen gas \((H_2)\) is added to unsaturated organic compounds, such as alkenes or alkynes, to form saturated compounds, such as alkanes.

Palladium, along with other transition metals such as platinum, nickel, and ruthenium, is frequently employed as a catalyst in hydrogenation reactions due to its ability to adsorb and activate hydrogen gas on its surface, facilitating the addition of hydrogen atoms to the unsaturated bonds in the reactant molecules.

The other options listed (barium, iron, and tungsten) are not commonly used as catalysts in hydrogenation reactions.