Which of the following order of CFSE is incorrect ? — Coordination Compounds Chemistry Question

💡 Solution & Explanation

Step 1: Determine the oxidation state and d-electron configuration of the metal in each complex: Co^2+ in (a) is 3d^7; Ni^2+ in (b) and (d) is 3d^8; Co^3+ in (c) is 3d^6. Step 2: In [Co(NH3)6]^3+, the strong-field NH3 ligands force all six d-electrons of Co^3+ to pair up in the lower t_2g orbitals, resulting in a low-spin t_2g^6 e_g^0 configuration. Step 3: Since there are zero unpaired electrons, [Co(NH3)6]^3+ is diamagnetic, while the other configurations retain unpaired electrons and are paramagnetic.