In which of the following equilibria does a change in the volume of the system not alter the number of moles?

Consider the reaction equilibrium,$2SO_{2(g)} + O_{2(g)} \rightleftharpoons 2SO_{3(g)}$; $\Delta H^\circ = -198 \ kJ$. On the basis of Le Chatelier's principle,the condition favourable for the forward reaction is

Does the number of moles of reaction products increase,decrease,or remain the same when each of the following equilibria is subjected to a decrease in pressure by increasing the volume?
$(a)$ $PCl_{5(g)} \rightleftharpoons PCl_{3(g)} + Cl_{2(g)}$
$(b)$ $CaO_{(s)} + CO_{2(g)} \rightleftharpoons CaCO_{3(s)}$
$(c)$ $3Fe_{(s)} + 4H_{2}O_{(g)} \rightleftharpoons Fe_{3}O_{4(s)} + 4H_{2(g)}$

For the equilibrium $2NO_{2(g)} \rightleftharpoons N_2O_{4(g)} + 21.9 \ kcal$,an increase in temperature will:

Explain the effect of concentration on equilibrium using the following experiment:
$Fe^{3+}_{(aq)} + SCN^{-}_{(aq)} \rightleftharpoons [Fe(SCN)]^{2+}_{(aq)}$
(Yellow) (Colourless) (Deep red)

In a vessel,the following two systems are in simultaneous equilibrium: $PCl_{5(g)} \rightleftharpoons PCl_{3(g)} + Cl_{2(g)}$ and $COCl_{2(g)} \rightleftharpoons CO_{(g)} + Cl_{2(g)}$. If some $CO$ is added to the vessel at constant volume,then at the new equilibrium: