Which one of the following complexes in an outer orbital complex?

• A

  $\left[\mathrm{Fe}(\mathrm{CN})_6\right]^{4-}$
• Correct answer
  B

  $\left[\mathrm{Ni}\left(\mathrm{NH}_3\right)_6\right]^{2+}$
• C

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

  $\left[\mathrm{Mn}(\mathrm{CN})_6\right]^{4-}$

Hence, the correct answer is option: 'B'.