Which of the following is an amphoteric substance?

What will be the conjugate acid-base pair in the reaction $HCl_{(aq)} + H_2O_{(aq)} \rightleftharpoons H_3O^{+}_{(aq)} + Cl^{-}_{(aq)}$?

The conjugate base of ${(CH_3)_2}\mathop N\limits^ + {H_2}$ is:

Write the conjugate base of the following: $HF, CH_{3}NH_{3}^{+}, H_{3}PO_{4}, HPO_{4}^{2-}$

Considering the following reactions,which pair of reactions shows that water has basic properties?
$(i) \ CO_2 + H_2O \rightleftharpoons H_2CO_3$
$(ii) \ NH_3 + H_2O \rightleftharpoons NH_4^+ + OH^-$
$(iii) \ HCl + H_2O \rightleftharpoons Cl^- + H_3O^+$

Identify the acids in the following reaction: $HCl_{(aq)} + H_2O_{(aq)} \rightleftharpoons H_3O^{+}_{(aq)} + Cl^{-}_{(aq)}$. Which of these acids is stronger?