CO(g) and H2(g) react to give different products in the presence of different catalyst. Catalyst selectivity is shown by these reactions. Catalyst selectivity is the ability of a catalyst to direct the reaction in such a way so that only one particular product is formed. ZnO and Cr2O3 catalyst is used to prepare methanol from CO(g) and H2(g). In Fischer Tropsch process, hydrocarbons are synthesized from CO(g) and H2(g) using Co, ThO2 catalyst.