The pH of a buffer solution obtained by the combination of a weak base (B) and its conjugate acid `(BH^+)` is 9. If the concentrations of B and `BH^+` in the buffer are 0.2(M) and 0.02(M) respectively, then find the ionisation constant of the weak base.

Explanation

`pH=pK_a+log([NaA])/([HA])` or , `