Solution:
\(\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]^{3-}\) has magnetic moment of a single unpaired electron whereas \(\left[\mathrm{FeF}_{6}\right]^{3}\) has a magnetic moment of five unpaired electrons. \(\left[\mathrm{CoF}_{6}\right]^{3}\) is paramagnetic with four unpaired electrons while \(\left[\mathrm{Co}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{3}\right]^{3}\) is diamagnetic. This anomaly is explained by valence bond theory in terms of formation of inner and outer orbital coordination entities. \(\left[\mathrm{Co}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{3}\right]^{3-}\) is an inner orbital complexes having \(d^{2} s p^{3}\) hybridization.
