Which of the following substances acts as a base when reacted with water?

Which of the following compounds are diprotic?

Among $CO_3^{2-}$,$OH^{-}$,$NH_3$ and $HCO_3^{-}$,the species that acts as a Bronsted acid as well as a Bronsted base,is

The position of equilibrium lies to the right in each of these reactions:
$N_2H_5^+ + NH_3 \rightleftharpoons NH_4^+ + N_2H_4$
$NH_3 + HBr \rightleftharpoons NH_4^+ + Br^{-}$
$N_2H_4 + HBr \rightleftharpoons N_2H_5^+ + Br^{-}$
Based on this information,what is the order of acidic strength?

Which of the following is the strongest conjugate base?

Write examples of weak acids and weak bases and give their ionic equilibrium in aqueous solution.