In which reaction is he underlined substance acting as a base?

$\mathrm{HNO}_{3}+\underline{\mathrm{H}_{2} \mathrm{SO}_{4}} \longrightarrow \mathrm{H}_{2} \mathrm{NO}_{3}^{+}+\mathrm{HSO}_{4}^{~~-}$

$\mathrm{HSiO-}^{-}+\underline{\mathrm{HCN}} \longrightarrow \mathrm{CN}^{-}+\mathrm{H}_{2} \mathrm{O}+\mathrm{SiO}_{2}$

$\mathrm{HNO}_{2}+\underline{\mathrm{HCO}_{3}^{-}} \longrightarrow \mathrm{H}_{2} \mathrm{O}=\mathrm{CO}_{2}+\mathrm{NO}_{2}^{-}$

$\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{O}^{-}+\underline {\mathrm{CH}_{2} \mathrm{ClCO}_{2} \mathrm{H}} \longrightarrow \mathrm{C} 6 \mathrm{H} 5 \mathrm{OH}+\mathrm{CH}_{2} \mathrm{ClCO}_{2}^{~-}$