Although `Cr^(3+)` and `Co^(2+)` ions have the same number of unpaired electrons but the magnetic moment of `Cr^(3+)` is 3.87 BM and that of `Co^(2+)` is 4.87 BM. Why?

Explanation

`Cr^(3+)` ion has symmetrical electronic configuration in the outermost orbit i.e., `3d^(3)`. In such ions there is no orbital configuration to magnetic moment. However, appreciable orbital contribution takes place in `Co^(2+)` with `3d^(7)` configuration.