Which of the following is the strongest conjugate base?

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 $NH_{3(aq)}$

In the following acid-base reactions,in which case can the backward reaction be favoured?

Derive $K_w = K_a \times K_b$ and $pK_w = pK_a + pK_b$ for a weak base $B$ and its conjugate acid $BH^{+}$.

Which of the following compounds cannot act as both a $Br\o nsted$ acid and a $Br\o nsted$ base?

The pair of compounds which cannot exist together in aqueous solution is:
$I.$ $NaH_2PO_4$ and $NaHCO_3$
$II.$ $Na_2CO_3$ and $NaHCO_3$
$III.$ $NaOH$ and $NaH_2PO_2$
$IV.$ $NaHCO_3$ and $NaOH$