(A)

Adsorption, whether it is chemisorption or physisorption, is an exothermic process. In physisorption, gas molecules are adsorbed onto the surface of the adsorbent by van der Waals forces. When the attractive forces between the gas and the solid adsorbent are stronger than those between the gas molecules themselves, energy is released, making the process exothermic.

In chemisorption, a chemical bond is formed between the adsorbent and the adsorbate. This bond formation releases energy, making the process exothermic.

Thus, Option A is correct.

(B)

At low temperatures, gases such as hydrogen or oxygen can accumulate on the solid surface (adsorbent) through a process called physisorption, which has a low enthalpy of adsorption (20-40 kJ/mol). With increasing temperature, oxygen or hydrogen can react with metal surfaces (adsorbent) to form metal oxides or metal hydrides, a process known as chemisorption, with an enthalpy of chemisorption between 80-240 kJ/mol.

Thus, Option B is correct.

(C)

Physisorption is a low enthalpy process that is favorable at low temperatures, while chemisorption has a high enthalpy process and occurs more readily at higher temperatures. Therefore, the statement that physisorption increases with increasing temperature and chemisorption decreases with increasing temperature is incorrect.

Thus, Option C is incorrect.

(D)

Chemisorption occurs at higher temperatures because the energy of the reactant molecules (adsorbate and adsorbent) must be sufficient to overcome the potential energy barrier to form the product. However, once chemical bonds are formed between the reactant molecules, a significant amount of energy is released. Therefore, chemisorption is more exothermic than physisorption.

Thus, Option D is correct.

Note : Physisorption arises due to weak forces of attraction between the adsorbent and the absorbent molecules.