The pH of buffer of `NH_4OH + NH_4Cl` - type is given by -

Mg^(2+) can be detected and esitimated in hard water by titrating with EDTA at pH=10 using NH_(4)OH+NH_(4)Cl buffer. End point is given by the apearance of blue colour. The indicator used is

Assertion : Buffer solutions are those which resist change in pH value on the addition of a small amount of acid or a base to it. Reason: Mixture of NH_4OH and NH_4 Cl acts as basic buffer.

Solution of 0.1 N NH_4OH and 0.1 NH_4Cl has has pH 9.25 Then pK_b of NH_4OH is