Adsorption is the phenomenon of attracting and retaining the molecules of a substance on the surface of a solid resulting into a higher concentration on the surface than in the bulk. The substance adsorbed is known as adsorbate and the substance on which adsorption takes place is called adsorbent. In physisorption adsorbate is held to the adsorbent by weak van der Waals forces and in chemisorption by strong chemical bond.

In the given reaction, catalyst used is

\(2H_2(g) + O_2(g) \longrightarrow 2H_2O (l)\)

Pt

The catalyst for the reaction between hydrogen and oxygen to form water is platinum (Pt).

The reaction between hydrogen and oxygen to form water is a very slow reaction under normal conditions. However, the presence of a catalyst, such as platinum, can greatly increase the rate of the reaction. Catalysts work by providing an alternative pathway for the reaction to occur, which has a lower activation energy than the uncatalyzed pathway.

Platinum is a very effective catalyst for this reaction because it has a strong affinity for both hydrogen and oxygen. This allows the hydrogen and oxygen molecules to adsorb onto the surface of the platinum catalyst, where they can come into close contact with each other and react to form water.

\(2H_2(g) + O_2(g)\overset{Pt}{\longrightarrow} 2H_2O (l)\)

The other options are incorrect because:

• Cu: Copper is not a very effective catalyst for this reaction.
• Ni: Nickel is a moderately effective catalyst for this reaction, but it is not as effective as platinum.
• Pd: Palladium is another effective catalyst for this reaction, but it is slightly less effective than platinum.

Therefore, the correct answer is platinum (Pt).