Answer:
Step-by-step explanation:
CN- (aq) + H₂0(l) = HCN(aq) + OH⁻ (aq)
In this reaction CN⁻ acts as base so
Kb = [ HCN][OH⁻] / [CN⁻ ]
Here water acts as medium so it is in excess hence its concentration remains constant . Hence its concentration is not taken into consideration.
(D) is the right choice.