The conjugate acid of $NH_3$ is

Addition of $Na_2CO_3$ to a solution of an oxide in water produces $CO_2$. This experiment indicates that

Which type of reaction occurs between $H_{2}SO_{4}$ and $HNO_{3}$ in nitration?

Which one of the following species acts as both Bronsted acid and base?

The enthalpy of neutralization of which of the following acids and bases is nearly $-13.6 \ kcal$?

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?