a) Activity: The ability of a catalyst to enhance the rate of a reaction is referred to as its activity. The main factor, chemisorption, determines a catalyst’s activity. The process should be neither too strong nor too weak when reactants are adsorbed on the catalyst surface. It should just be powerful enough to activate the catalyst.

b) Selectivity: The capacity of a catalyst to control a reaction to produce a certain product is referred to as selectivity. For example, we can produce different products for the reaction between Hydrogen and Carbon monoxide by using different catalysts.

(i) $CO(g)+3H2(g)\xrightarrow{Ni}CH4(g)+H2O(g)$

(ii) \[CO(g)+2H2(g)\xrightarrow{CuZnO-CrO3}CH3OH(g)\]