Which of the following ions can act as both an acid and a base?

Which one of the following is not an amphoteric substance?

Lewis acids are those substances which:

$HSO_4^-$ is the conjugate base of

Which solution contains the maximum number of $H^{+}$ ions?

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