Among the free ions Fe^2+, Co^2+, Ni^2+ and Cu^2+, the highest spin-only magnetic moment is shown by

JEE Main levelSingle correct optionDifficulty 2 of 3df020

Among the free ions $Fe X^{2 +}$ , $Co X^{2 +}$ , $Ni X^{2 +}$ and $Cu X^{2 +}$ , the highest spin-only magnetic moment is shown by

Configurations:

d^{6}

d^{7}

d^{8}

and

d^{9}

with 4, 3, 2 and 1 unpaired electrons. The moments are 4.90, 3.87, 2.83 and 1.73 BM, so

Fe X^{2 +}

is highest.