Question

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

• A. $\left[Fe\left(CN\right)_{6}\right]^{4-} $
• B. $ \left[Mn\left(CN\right)_{6}\right]^{4-} $
• C. $ \left[Co\left(NH_3\right)_{6}\right]^{3+} $
• D. $ \left[Ni\left(NH_{3}\right)_{6}\right]^{2+} $

Answer 1

Answer: (D)

In this case, $NH _{3}$ is a strong ligand but electrons remain unpaired since only one orbital is left vacant in $3 d$. Thus,