An unknown 3d transition metal ion M ³⁺ forms an octahedral complex with a weak field ligand, exhibiting a spin-only magnetic moment of approximately 4.9 BM . The same metal ion forms a different octahedral complex with a strong field ligand, which is found to be completely diamagnetic. The Crystal Field Stabilization Energy (CFSE) of the diamagnetic complex in terms of ₀ (ignoring pairing energy) is :

Step-by-step solution

The spin-only magnetic moment of the weak field complex is 4.9 BM . Using the formula = n(n+2) , we get n = 4 unpaired electrons. For an octahedral complex of a M ³⁺ ion with a weak field ligand (high-spin), having 4 unpaired electrons implies the d -electron configuration could be either d⁴ ( t_ 2g ³ e_ g ¹ ) or d⁶ ( t_ 2g ⁴ e_ g ² ). The strong field complex of the same metal ion is diamagnetic, meaning it has 0 unpaired electrons. If the metal were d⁴ , its strong field (low-spin) configuration would be t_ 2g ⁴