Milk of magnesia contains a base called

$$\begin{gathered} \mathrm{A}: {\mathrm{H}}_2{\mathrm{SO}}_4 \\ \mathrm{B}: {\mathrm{H}}_2{\mathrm{SO}}_3 \\ \mathrm{C}: {\mathrm{H}}_{2}S \end{gathered}$$

(Enter your correct answer as $\mathrm{A}, \mathrm{B} \mathrm{or} \mathrm{C}$)

Identify chemical formulae of the following:
Nitric acid

$$\begin{gathered} \mathrm{A}: {\mathrm{H}}_2{\mathrm{SO}}_4 \\ \mathrm{B}: {\mathrm{HNO}}_3 \\ \mathrm{C}: {\mathrm{HNO}}_2 \end{gathered}$$

(Enter your correct answer as $\mathrm{A}, \mathrm{B} \mathrm{or} \mathrm{C}$)

$$\begin{gathered} \mathrm{A}: {\mathrm{Na}}_2{\mathrm{CO}}_3 \\ \mathrm{B}: {\mathrm{NaHCO}}_3 \\ \mathrm{C}: {\mathrm{HNO}}_2 \end{gathered}$$

(Enter your correct answer as $\mathrm{A}, \mathrm{B} \mathrm{or} \mathrm{C}$)