The activity of a catalyst pellet is defined as the ratio of ___
(a) Rate of adsorption of reactants to the catalyst surface to the rate at which the catalytic pellet converts the reactant
(b) Rate at which the catalytic pellet converts the reactant to the rate of adsorption of reactants to the catalyst surface
(c) Rate at which the catalytic pellet converts the reactant to the rate of reaction with a fresh pellet
(d) The rate of reaction with a fresh pellet to the rate at which the catalytic pellet converts the reactant