In aqueous solution,$Na_2SO_3$ is oxidized by air,but $Na_3AsO_3$ is not. However,when air is passed through a solution containing both $Na_2SO_3$ and $Na_3AsO_3$,both are oxidized. This is an example of:

Which statement is correct regarding a catalyst?

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.

Two percent of ethanol is added during the oxidation of chloroform to stop the formation of carbonyl chloride. In this reaction,ethanol acts as:

Adsorption theory is applicable for

$A$ catalyst is a substance which