The conjugate base of $HPO_4^{2-}$ is .....

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

Match the following species with their respective conjugate acids:

Species	Conjugate acid
$ (a) NH_{3} $	$ (i) H_{2}CO_{3} $
$ (b) HCO_{3}^{-} $	$ (ii) H_{3}O^{+} $
$ (c) H_{2}O $	$ (iii) NH_{4}^{+} $
$ (d) HSO_{4}^{-} $	$ (iv) H_{2}SO_{4} $

If the $pK_b$ of the fluoride ion $(F^-)$ at $25^{\circ}C$ is $10$,what is the ionization constant $(K_a)$ of hydrofluoric acid $(HF)$ at the same temperature?

Which of the following is a Lewis base?

The conjugate base of ${(CH_3)_2}\mathop N\limits^ + {H_2}$ is: