Ammonia gas dissolves in water to form $NH_4OH$. In this reaction,water acts as:

What is the conjugate acid of $HPO_4^{2-}$?

Which one is not an acid salt?

The dissociation constant of a weak acid $HA$ is $1.8 \times 10^{-4}$. Calculate the dissociation constant of its conjugate base $A^{-}$.

The correct order of basic strength of the following compounds is:
$(I)$ $KOH$
$(II)$ $Zn(OH)_2$
$(III)$ $HNO_3$
$(IV)$ $Ca(OH)_2$

The number of species among the following that can act both as Bronsted acids and bases is $HCl, ClO_4^{-}, OH^{-}, H^{+}, H_2O, HSO_4^{-}, SO_4^{2-}, H_2SO_4, Cl^{-}$.