A popular buffer solution consists of carbonate $(CO_3^{2-})$ and hydrogen carbonate $(HCO_3^-)$ conjugate acid-base pair. Which, if any, of the following such buffers has the highest buffer capacity?
0. 5 M $CO_3^{2-}$ and 0.5 M $HCO_3^-$
1. 9 M $CO_3^{2-}$ and 0.1 M $HCO_3^-$
They all have the same buffer capacity.
2. 1 M $CO_3^{2-}$ and 0.9 M $HCO_3^-$
3. 1 M $CO_3^{2-}$ and 0.1 M $HCO_3^-$