b
Spin only magnetic moment \(=\sqrt{n(n+2)}\) B.M. Where, \(n=\) no. of unpaired electrons. Given, \(\sqrt{n(n+2)}=2.84\)
or, \(n(n+2)=8.0656\)
or, \(n=2\)
In an octahedral complex, for a \(d^{4}\) configuration in a strong filed ligand, number of unpaired electrons \(=2\)