Adsorption is a surface phenomenon and it differs feom adsorption which occurs throughout the body of the substance which absorbs. In physisorption, the attractive forces are mainly van der Waals' forces while in chemisorption actual bonding occurs between the particles of adsorbent and adsorbente. Generally, easily liquefying gases are adsorbed more easily on the surface of a solid as compared to teh gases whihc are liquefied with difficult. Adsorption increases with the increases in pressure and decreases as the temperature is increases.
According to adsorption theory of catalysis, the speed of the reaction increases because

Options

A. the concentration of the reactant molecules at the active centres of the catalyst becomes high due to adsorption,
B. in the process of adsorption, the activation energy of the molecules becomes large.
C. adsorption produces heat which increases the speed of the reaction
D. adsorption lowers the activation energy of the reaction.