Platinised asbestos helps in the formation of $SO_3$ from $SO_2$ and $O_2$. But,if even a small amount of $As_2O_3$ is present,the platinised asbestos does not help in the formation of $SO_3$. $As_2O_3$ acts here as

In the contact process for the manufacture of $H_2SO_4$, the arsenic purifier used in the industrial plant contains:

The number of correct statements about modern adsorption theory of heterogeneous catalysis from the following is ..........
$A.$ The catalyst is diffused over the surface of reactants.
$B.$ Reactants are adsorbed on the surface of the catalyst.
$C.$ Occurrence of chemical reaction on the catalyst's surface through formation of an intermediate.
$D.$ It is a combination of intermediate compound formation theory and the old adsorption theory.
$E.$ It explains the action of the catalyst as well as those of catalytic promoters and poisons.

Explain the shape selective catalysis by zeolites.

In Haber's process for the manufacture of ammonia:

In a chemical reaction,a catalyst . . . . .