Select the correct statement from the following:

Consider the following reactions. In which cases is product formation favoured by decreased temperature?
$(a) \ N_{2(g)} + O_{2(g)} \rightleftharpoons 2NO_{(g)}; \ \Delta H^o = 181 \ kJ$
$(b) \ 2CO_{2(g)} \rightleftharpoons 2CO_{(g)} + O_{2(g)}; \ \Delta H^o = 566 \ kJ$
$(c) \ H_{2(g)} + I_{2(g)} \rightleftharpoons 2HI_{(g)}; \ \Delta H^o = -9.4 \ kJ$
$(d) \ H_{2(g)} + F_{2(g)} \rightleftharpoons 2HF_{(g)}; \ \Delta H^o = -541 \ kJ$

Explain the effect of pressure change on an equilibrium system with suitable examples.

For the reaction $aA + bB \rightleftharpoons cC + dD$,if the equilibrium shifts in the backward direction at low pressure and high temperature,which of the following is correct?

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?
$(a) \quad PCl_{5(g)} \longleftrightarrow PCl_{3(g)} + Cl_{2(g)}$
$(b) \quad CaO_{(s)} + CO_{2(g)} \longleftrightarrow CaCO_{3(s)}$
$(c) \quad 3Fe_{(s)} + 4H_2O_{(g)} \longleftrightarrow Fe_3O_{4(s)} + 4H_{2(g)}$

When $NaNO_{3(s)}$ is heated in a closed vessel,$O_{2(g)}$ is released and $NaNO_{2(s)}$ remains. The equilibrium is: $NaNO_{3(s)} \rightleftharpoons NaNO_{2(s)} + 1/2 O_{2(g)}$. Which of the following is correct?