Chemistry - Ionic Equilibrium Question with Solution | TestHub

Key Idea Bronsted acid is a substance which has a tendency to donate proton. Bronsted base is a substance which has a tendency to accept proton. HCl can act as Bronsted acid becuase it can only donate proton. $$\mathrm{HCl}+{\mathrm{H}}_2\mathrm{O}\rightleftharpoons {\mathrm{H}}_3{\mathrm{O}}^{+}+{\mathrm{Cl}}^{-}$$ The remaining options contains substances which act both as Bronsted acid and Bronsted base. $$\begin{array}{rl}{\mathrm{HCO}}_3^{-}+{\mathrm{HCO}}_3^{-}& \rightleftharpoons {\mathrm{H}}_2{\mathrm{CO}}_3+{\mathrm{CO}}_3^{2-}\\ {\mathrm{NH}}_3+{\mathrm{NH}}_3& \rightleftharpoons {\mathrm{NH}}_4^{+}+{\mathrm{NH}}_2^{-}\\ {\mathrm{HSO}}_4^{-}+{\mathrm{HSO}}_4^{-}& \rightleftharpoons {\mathrm{H}}_2{\mathrm{SO}}_4+{\mathrm{SO}}_4^{2-}\end{array}$$ Thus, option (3) is correct.