Which one of the following complexes is an outer orbital complex? (Atomic numbers $\mathrm{Mn}=25, \mathrm{Fe}=26, \mathrm{Co}=27$, $\mathrm{Ni}=28)$

• A

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

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

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

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

Solution

The complex in which nd orbitals are used in hybridisation, are called outer orbital complex. (a) $\left[\mathrm{Fe}(\mathrm{CN})_6\right]^{4-}=$
(b) $\left[\mathrm{Mn}(\mathrm{CN})_6\right]^{4-}=$
(c) $\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{3+}=$
(d) $\left[\mathrm{Ni}\left(\mathrm{NH}_3\right)_6\right]^{2+}=$

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