For the equilibrium that exists in an aqueous solution of nitrous acid (HNO2, a weak acid), the equilibrium constant expression is:_______a. K = [H+][NO2-]/[HNO2] b. K = [H+][N3+][O2-]^2/ [HNO2]c. K= [H+][NO2-] d. K = [H+]^2[NO-]/[HNO2]