Which one of the following complexes is an inner orbital complex?

[Fe(CN)₆]^4–

The correct answer is option 2. [Fe(CN)₆]^4–

The given complex is [Fe(CN)₆]^4–

Let the oxidation number of the central metal atom be \(x\)

\(x + 6(−1) = −4\)

\(⇒ x= 2\)

Thus, the electronic configuration of the central metal ion, i.e., Fe in +2 oxidation state is

We know, \(CN^-\) is a strong field ligand that leads to the pairing of the 3d electron. So, the configuration becomes:Here, we have six \(CN^-\) ligands that arrange themselves in the two empty 3d orbital, 1 4s orbital, and the 3 4p orbital thus forming a \(d^2sp^3\) hybridization and forms an inner orbital complex.