Consider a solution consisting of the following two buffer systems: H2CO3 HCO3 – + H+ pKa = 6.4 H2PO4 – HPO4 2– + H+ pKa = 7.2 At pH 6.4, which one of the following is true of the relative amounts of acid and conjugate base present? a. [H2CO3 ] > [HCO3 – ] and [H2PO4 – ] > [HPO4 2–] b. [H2CO3 ] = [HCO3 – ] and [H2PO4 – ] > [HPO4 2–] c. [H2CO3 ] = [HCO3 – ] and [HPO4 2–] > [H2PO4 – ] d. [HCO3 – ] > [H2CO3 ] and [HPO4 2–] > [H2PO4 – ] e. [H2CO3 ] > [HCO3 – ] and [HPO4 2–] > [H2PO4 – ]