$A, B, C$ and $D$ are some compounds. The entnalpy of formation of $A(g), B(g), C(g)$ and $D(g)$ is $9.7,-110,81$ and $-393 \mathrm{~kJ} \mathrm{~mol}^{-1}$ respectively. What is $\Delta_r H$

(in $\mathrm{kJ} \mathrm{mol}^{-1}$ ) for the given reaction ?

$$ A(g)+3 B(g) \longrightarrow C(g)+3 D(g) $$

At equilibrium of the reaction,

$$ A_2(g)+B_2(g) \rightleftharpoons 2 A B(g) $$

The concentrations of $A_2, B_2$ and $A B$ respectively are $15 \times 10^{-3} \mathrm{M}, 2.1 \times 10^{-3} \mathrm{M}$, and $1.4 \times 10^{-3} \mathrm{M}$ in a sealed vessel at 800 K . What will be $K_p$ for the decomposition of $A B$ at same temperature ?

Which of the following when added to 20 mL of a 0.01 M solution of HCl would decrease its pH ?