16. In the carbonate buffering system, the pKa1=6.3 and pKa2=10.3. At pH 10.3, which of the following is true? a) The concentrations of HCO3- and CO3^2- are equal and the

concentration of H2CO3 is close to zero. b) The concentrations of HCO3- and H2CO3 are equal and the concentration of CO3^2- close to zero. c) The concentrations of H2CO3 and CO3²- are equal and the concentration of HCO3- is close to zero. d) The concentrations of H2CO3, HCO3- and CO3²- are essentially equal. e) The concentrations of HCO3¯ is at a maximum and the concentration of CO3²- and H2CO3 are close to zero.