Which of the following pairs consists entirely of diamagnetic, inner-orbital complexes?

Step-by-step solution

To be a diamagnetic inner-orbital complex, the central metal must use (n-1)d orbitals for hybridization (typically d^2sp^3 ) and have zero unpaired electrons. For [CoF₆ ]³⁻ : Co³⁺ is 3d^6 . F^- is a weak field ligand, so it forms a high-spin outer-orbital complex ( sp^3d^2 ) with 4 unpaired electrons. For [Fe(CN)₆ ]³⁻ and [Ru(NH₃)₆ ]³⁺ : Fe³⁺ is 3d^5 and Ru³⁺ is 4d^5 . Both form inner-orbital complexes, but a d^5 strong-field configuration ( t_ 2g ^5 ) has 1 unpaired electron, making them paramagnetic. For [Mn(CN)₆