A complex of ${\text{Fe}}^{2+}$ has magnetic moment value of 4.89 B.M. The number of electrons in the $t_{2g}$ level of ${\text{Fe}}^{2+}$ is ___________

$\mu =4.89=\sqrt{n(n+2)}\Rightarrow n=4$

Since, ${\text{Fe}}^{2+}$ has four unpaired electrons so, its configuration will be

Hence, it is a weak field complex.
In weak field complexes, first the $t_{2g}$ and $e_g$ levels are singly occupied and then the pairing of electrons in $t_{2g}$ level takes place. Thus, there are 4 electrons in $t_{2g}$ level.