. According to the adsorption theory of catalysis, the speed of the reaction increases because

(a)  adsorption produces heat which increases the speed of the reaction

(b)  adsorption lowers the activation energy of the reaction.

(c)  the concentration of reactant molecules at the active centres of the catalyst becomes high due to adsorption   

(d)  nin the process of adsorption, the activation energy of the molecules become large