Among the following pairs of coordination complexes, identify the pair where the difference in the number of unpaired electrons between the two complexes is exactly 3.

Step-by-step solution

Let n be the number of unpaired electrons. Option 1: [Fe(H₂O)₆]³⁺ contains Fe³⁺ ( 3d^5 ). H₂O is a weak field ligand, so n = 5 . [Fe(CN)₆]³⁻ contains Fe³⁺ ( 3d^5 ). CN^- is a strong field ligand, so t_ 2g ^5 e_g^0 , giving n = 1 . Difference = 5 - 1 = 4 . Option 2: [Mn(H₂O)₆]²⁺ contains Mn²⁺ ( 3d^5 ). H₂O is a weak field ligand, so n = 5 . [Mn(CN)₆]³⁻ contains Mn³⁺ ( 3d^4 ). CN^- is a strong field ligand, so t_ 2g ^4 e_g^0 , giving n = 2 . Difference = 5 - 2 = 3 . Option 3: [CoF₆]³⁻ contains Co³⁺ ( 3d^6 ). F^- is a