The equilibrium constant for this reaction is approximately 10^-3 ${\mathrm{HPO}}_{4\left(\mathrm{aq}\right)}^{2-}+{\mathrm{HCO}}_{3\left(\mathrm{aq}\right)}^{-}\rightleftharpoons {\mathrm{H}}_2{\mathrm{PO}}_{4\left(\mathrm{aq}\right)}^{-}+{{\mathrm{CO}}_3^{2-}}_{\left(\mathrm{aq}\right)}$  Which is the strongest conjugate base in this reaction?

• A

  ${\text{HPO}}_4^{2-} (\mathrm{aq})$

• B

  ${\mathrm{HPO}}_3^{-}(\mathrm{aq})$

• C

  ${\mathrm{H}}_2{\mathrm{PO}}_4^{-}\left(\mathrm{aq}\right)$

• D

  ${\mathrm{CO}}_3^{2-}\left(\mathrm{aq}\right)$