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

An acid is a compound which furnishes ($Bronsted-Lowry$ concept):

Among the following,the weakest base is

Which among the following is a correct conjugate acid-base pair for the equation stated below?
$HCl + NH_3 \rightleftharpoons NH_4^{+} + Cl^{-}$

$HF + HClO_4 \rightleftharpoons H_2F^{+} + ClO_4^-$ and $H_2O + H_2PO_4^- \rightleftharpoons H_3O^{+} + HPO_4^{2-}$ Select the group of acidic species present on the right side of the equilibrium.

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 $NaOH$