$HNO_3$ in liquid hydrogen fluoride behaves as:

The conjugate base of $NH_4^{+}$ is

The correct decreasing order of basic strength of $H_2O$,$NH_3$,$OH^{-}$,and $NH_2^{-}$ is:

$A$ solution of ammonia in water contains

Three reactions involving $H_2PO_4^-$ are given below :
$(i) \; H_3PO_4 + H_2O \rightarrow H_3O^{+} + H_2PO_4^-$
$(ii) \; H_2PO_4^- + H_2O \rightarrow HPO_4^{2-} + H_3O^{+}$
$(iii) \; H_2PO_4^- + OH^{-} \rightarrow H_2O + HPO_4^{2-}$
In which of the above does $H_2PO_4^-$ act as an acid?

The conjugate acid of $NH_2^-$ is