Which of the following will produce a buffer solution when mixed in equal volumes?

The ionisation of hydrochloric in water is given below:

$\mathrm{HCl}\left(\mathrm{aq}\right) + {\mathrm{H}}_2\mathrm{O} \left(\mathrm{l}\right) \rightleftharpoons {\mathrm{H}}_3{\mathrm{O}}^{+} \left(\mathrm{aq}\right) + {\mathrm{Cl}}^{-} \left(\mathrm{aq}\right)$

Label two conjugate acid-base pairs in this ionisation.

Ionisation constant of a weak base $\mathrm{MOH}$, is given by the expression

${\mathrm{K}}_{\mathrm{b}}=\frac{\left[{\mathrm{M}}^{+}\right]\left[{\mathrm{OH}}^{-}\right]}{\left[\mathrm{MOH}\right]}$

Values of ionisation constant of some weak bases at a particular temperature are given below:

Arrange the bases in decreasing order of the extent of their ionisation at equilibrium. Which of the above base is the strongest?