What is the correct electronic configuration of the central atom in ${\text{K}}_{\text{4}}\left[\text{Fe}{\left(\text{CN}\right)}_{\text{6}}\right]$ based on crystal field theory ?

Configuration of  Fe⁺² :  $3{\mathrm{d}}^{6}4{\mathrm{s}}^0$

Configuration of ${\mathrm{K}}_4\left[\mathrm{Fe}{\left(\mathrm{CN}\right)}_6\right]$ : ${\mathrm{t}}_{2\mathrm{g}}^6{\mathrm{e}}_{\mathrm{g}}^0$

Since -CN is a strong field ligand, pairing takes place against to Hund's rule.