The dissociation constant of a monobasic acid which is 3.5% dissociated in N20 solution at 20oC is

Concentration of acid = N20 = 0.05 NOut of 100 molecules, 3.5 molecules has been dissociated α=35100 =0.035                                                               Ka= Cα21-α = 0.05× 0.03521-0.035                       = 6.34× 10-5