The correct decreasing order of the spin-only magnetic moments for the complexes [ Mn ( CN )₆ ]³⁻ , [ Fe ( CN )₆ ]³⁻ , [ Co ( C ₂ O ₄)₃ ]³⁻ , and [ Ni ( NH ₃)₆ ]²⁺ is :

Step-by-step solution

To find the spin-only magnetic moment, we must determine the number of unpaired electrons ( n ) in each complex. 1. [ Mn ( CN )₆ ]³⁻ : The oxidation state of Mn is +3. The electronic configuration of Mn ³⁺ is 3d^4 . Since CN ^- is a strong field ligand, pairing occurs, resulting in a t_ 2g ^4 e_g^0 configuration. Thus, n = 2 . 2. [ Fe ( CN )₆ ]³⁻ : The oxidation state of Fe is +3. The electronic configuration of Fe ³⁺ is 3d^5 . CN ^- is a strong field ligand, causing pairing to give a t_ 2g ^5 e_g^0 configuration.