In which of the following octahedral complexes of Co (at. no. 27),will the magnitude of ${\mathrm{\Delta }}_{\mathrm{o}}$ be the highest?

• A

  ${\left[\mathrm{Co}(\mathrm{CN}{)}_6\right]}^{3-}$

• B

  ${\left[\mathrm{Co}{\left({\mathrm{C}}_2{\mathrm{O}}_4\right)}_3\right]}^{3-}$

• C

  ${\left[\mathrm{Co}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6\right]}^{3+}$

• D

  ${\left[\mathrm{Co}{\left({\mathrm{NH}}_3\right)}_6\right]}^{3+}$