The conjugate base of $H_{2}PO_{4}^{-}$ is:

If $pK_b$ for fluoride ion $(F^-)$ at $25\,^{\circ}C$ is $10.83$,the ionisation constant $(K_a)$ of hydrofluoric acid $(HF)$ in water at this temperature is:

The compound that is not a Lewis acid is

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

Conjugate base for Bronsted acids $H_{2}O$ and $HF$ are

What will be the $pH$ of the solution if $BCl_3$ is dissolved in water?