$A$ catalyst remains unchanged at the end of the reaction regarding

Which among the following can be explained by adsorption theory?

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

The correct statements about Zeolites are:
$(I)$ They are good shape-selective catalysts.
$(II)$ They contain $Al-O-Si$ framework.
$(III)$ They are not found in nature.
$(IV)$ They are used as catalysts for cracking hydrocarbons in the petrochemical industry.

$A$ catalyst increases the rate of reaction because it

The process which is catalysed by one of the products is called