Which one of the following shows highest magnetic moment?

Step-by-step solution

Atomic number of Fe (26)=[ Ar ] 3 d⁶ 4 s² Fe ²⁺=[ Ar ] 3 d⁶ 4 s⁰ Number of unpaired electrons =4 For Co ²⁺=[ Ar ] 3 d⁷ Number of unpaired electrons =3 It shows highest magnetic moment. As magnetic moment depends on number of unpaired electrons. For Cr ³⁺=[ Ar ] 3 d³ Number of unpaired electrons =3 For Ni ⁺=[ Ar ] 3 d⁸ Number of unpaired electrons =2