Hydrogenation of an unsaturated hydrocarbon to a saturated one is commonly carried out using which catalyst?

The correct option is Nickel or palladium.

Explanation

Hydrogenation is a chemical reaction involving the addition of dihydrogen ($H_2$) across the multiple bonds (double or triple bonds) of unsaturated hydrocarbons (alkenes or alkynes) to form saturated hydrocarbons (alkanes). This process is kinetically slow at room temperature and requires a catalyst to proceed at an appreciable rate.

Analysis of Options:

• Nickel or palladium is correct: The hydrogenation process is catalysed by finely divided transition metals such as Nickel (Ni), Palladium (Pd), or Platinum (Pt). These metals adsorb hydrogen gas on their surface, activating the hydrogen bond and facilitating its addition to the unsaturated hydrocarbon. For example, the Sabatier-Senderens reaction specifically utilizes Nickel at elevated temperatures.
• Silica gel is incorrect: Silica gel is a porous form of silicon dioxide used primarily as a desiccant (drying agent) to absorb moisture or as a stationary phase in chromatography. It does not catalyse hydrogenation.
• Alumina alone is incorrect: Alumina ($Al_2O_3$) is typically used as a dehydrating agent (e.g., converting alcohols to alkenes) or as a support material for other catalysts, but it is not the primary catalyst for hydrogenation.
• Copper sulphate is incorrect: Copper sulphate is a salt commonly used as a fungicide, algicide, or in electroplating. It does not function as a catalyst for the hydrogenation of hydrocarbons.

Key Takeaway: Catalytic hydrogenation converts unsaturated hydrocarbons into saturated alkanes using finely divided metals like Nickel, Palladium, or Platinum to lower the activation energy of the reaction.