$NH_3$ gas dissolves in water to give $NH_4OH$. In this reaction,water acts as a/an ...... .

Identify the conjugate acid-base pair respectively from the following equilibrium reaction.
$HPO_{4(aq)}^{2-} + H_2O_{(\ell)} \rightleftharpoons PO_{4(aq)}^{3-} + H_3O_{(aq)}^{+}$

Which of the following is a conjugate acid-base pair?

When a solution of $NaOH$ is left exposed to air for a few hours,what happens?

Which are the conjugate bases of the strong acids $HClO_4$,$H_2SO_4$,$HNO_3$,and $HPO_4^{2-}$? Are they strong or weak?

Arrange the following ions in the correct order of their acidity: $(i) \, HCO_3^-, (ii) \, H_3O^+, (iii) \, HSO_4^-, (iv) \, HSO_3F$.