Which of the following compounds acts as a $Lewis$ base?

The dissociation of $H_3PO_4$ occurs in how many stages?

The conjugate base of $H_3O^{+}$ is

Which one of the following acids is the weakest?

The $H^{+}$ ion is a ...... .

Which two sets of reactants best represent the amphoteric character of $Zn(OH)_2$?
Set $1$ : $Zn(OH)_{2(s)}$ and $OH^{-}_{(aq)}$
Set $2$ : $Zn(OH)_{2(s)}$ and $H_2O_{(l)}$
Set $3$ : $Zn(OH)_{2(s)}$ and $H^{+}_{(aq)}$
Set $4$ : $Zn(OH)_{2(s)}$ and $NH_{3(aq)}$