The role of a catalyst in a reversible reaction is to

In which of the following reactions will a change in pressure not affect the rate of reaction?

What would happen to a reversible reaction at equilibrium when an inert gas is added while the pressure remains unchanged?

Consider the heterogeneous equilibrium in a closed container:
$NH_4HS_{(s)} \rightleftharpoons NH_{3(g)} + H_2S_{(g)}$
If more $NH_4HS_{(s)}$ is added to the equilibrium,what will be the effect on the system?

Explain the effect of adding $(i)$ Oxalic acid $(H_2C_2O_4)$,$(ii)$ $HgCl_2$,and $(iii)$ Potassium thiocyanate $(KSCN)$ on the equilibrium reaction: $Fe^{3+}(aq) + SCN^-(aq) \rightleftharpoons [Fe(SCN)]^{2+}(aq)$ (deep red color).

Adding an inert gas to the system $N_{2(g)} + 3H_{2(g)} \rightleftharpoons 2NH_{3(g)}$ at equilibrium at constant volume will lead to: