Which of the following ions has a 'spin only' magnetic moment of 3.87 BM ?

Step-by-step solution

The spin-only magnetic moment ( ) is given by the formula = n(n+2) BM , where n is the number of unpaired electrons. Given = 3.87 BM : n(n+2) = 3.87 n(n+2) 15 This gives n = 3 unpaired electrons. Now, let us check the electronic configuration of the given ions: Ni ²⁺ ( Z=28 ): [ Ar ] 3d^8 2 unpaired electrons. Fe ²⁺ ( Z=26 ): [ Ar ] 3d^6 4 unpaired electrons. Cu ²⁺ ( Z=29 ): [ Ar ] 3d^9 1 unpaired electron. Co ²⁺ ( Z=27 ): [ Ar ] 3d^7 3 unpaired electrons. Therefore, Co ²⁺ has 3 unpaired electrons and a magnetic mo