Determine the acid dissociation constant Ka for a 0.010 < nitrous acid solution that has a pH of 2.70. Nitrous acid is a weak monoprotic acid and the equilibrium equation of iterest is: HNO2 (aq) + H2O <----> (equilibrium) H3O^+ (aq) + NO2^- A.) 4.0 x 10^-4 b.) 5.0 x 10^-4 c.) 2.0 x 10^-3 I know the answer is B but I do not understand how to get.