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

Which acid is present in tomatoes?

According to the $Br\o nsted-Lowry$ theory,water is a/an:

$CH_3COOH_{(aq)} + H_2O_{(l)} \rightleftharpoons H_3O^{+}_{(aq)} + CH_3COO^{-}_{(aq)}$. Between $H_2O$ and $CH_3COO^{-}$,which one is the weaker base?

Which of the following species are only Lewis acids but not Bronsted acids from $CO_{2}$,$BCl_{3}$,$NH_{3}$,$CH_{3}NH_{2}$,$NO_{2}^{+}$,and $C_{6}H_{5}NH_{3}^{+}$?

Identify the conjugate acid-base pairs in the reaction: $NH_{3(aq)} + H_2O_{(l)} \rightleftharpoons NH_{4(aq)}^+ + OH_{(aq)}^-$