The number of dissociable protons in "orthophosphoric acid" is

Which is the strongest of the following acids?

The strongest base from the following species is

Give the conjugate acid and conjugate base of the following:
$(i)$ $(CH_3)_2NH$
$(ii)$ $HPO_4^{2-}$
$(iii)$ $HS^{-}$

Conjugate acid of $HPO_4^{2-}$ is

Identify the conjugate acid-base pair respectively from the following equilibrium reaction.
$HPO_{4(aq)}^{2-} + H_2O_{(\ell)} \rightleftharpoons PO_{4(aq)}^{3-} + H_3O_{(aq)}^{+}$