A diprotic acid, H2A, has the following ionization constants: Ka1 = 1.1 multiplied by 10-3 and Ka2 = 2.5 multiplied by 10-6. In order to make up a buffer solution of pH 5.80, which combination would you choose, NaHA/H2A or Na2A/NaHA? What is the pKa of the acid component?