During adsorption, there is always a decrease in surface energy which appears as heat. In other words, adsorption is an exothermic process. Physisorption may transform into chemisorption at high temperature. For example, dihydrogen is first adsorbed on Ni by van der Waals forces, molecules of hydrogen then dissociate to form hydrogen atoms which are held on the surface by chemisorption. Low temperature is favourable for physisorption. It decreases with increase of temperature, high temperature is favourable for chemisorption, it increases with increase of temperature. Energy of adsorption is high in chemisorption which is about 80–240 KJ/mol as compared to physiosorption where the energy is about 20–40 KJ/mol. Hence, the statements given in options (A), (B) and (D) are correct.