$H_2C=CH_2 + O_2 \xrightarrow{\text{aqueous medium}} CH_3CHO$. What is the catalyst used in the above green reaction?

Which catalyst is used in the reaction $2KClO_3 \to 2KCl + 3O_2$?

Which one of the following acts as an autocatalyst during the titration of $KMnO_4$ and oxalic acid in the presence of dilute $H_2SO_4$?

Match the catalyst (Column-$I$) with products (Column-$II$)

Column-$I$ Catalyst	Column-$II$ Product
$(a)$ $V_2O_5$	$(i)$ Polyethylene
$(b)$ $TiCl_4/Al(Me)_3$	$(ii)$ Ethanal
$(c)$ $PdCl_2$	$(iii)$ $H_2SO_4$
$(d)$ Iron oxide	$(iv)$ $NH_3$

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:

Protons accelerate the hydrolysis of esters. This is an example of