Which of the following can be explained by Le Chatelier's principle?

In which of the following reactions,increase in the volume at constant temperature does not affect the number of moles at equilibrium?

Consider the reaction $HCN_{(aq)} \Leftrightarrow H_{(aq)}^{+} + CN_{(aq)}^{-}$. At equilibrium,the addition of $CN_{(aq)}^{-}$ would

Two systems $PCl_{5(g)} \rightleftharpoons PCl_{3(g)} + Cl_{2(g)}$ and $COCl_{2(g)} \rightleftharpoons CO_{(g)} + Cl_{2(g)}$ are in equilibrium simultaneously in a container of constant volume. If some $CO_{(g)}$ is added to the container at constant volume,then at the new equilibrium:

Explain the effect of a catalyst on chemical equilibrium with examples.

The equilibrium constant $K$ and reaction quotient $Q$ are in the ratio $K : Q = 0.33 : 1$. This means that: