$\mathrm{Fe}(26)=3 \mathrm{d}^{6} 4 s^{2}$
$\mathrm{Fe}^{+2}=3 \mathrm{d}^{6}$
In presence of $\mathrm{SFL}\;\;\; 3 \mathrm{d}^{6} \rightarrow \mathrm{t}_{2 \mathrm{g}}^{6} \mathrm{e}_{\mathrm{g}}^{\circ}$
$(I)\,[Cr(NO_3)_3(NH_3)_3]$ $(II)\, K_3[Fe(C_2O_4)_3]$ $(III)\,[CoCl_2(en)_2]^+$ $(IV)\, [CoBrCl(ox)_2]^{3-}$
$(P)\, Fe(CO)_5\,\,\, (Q)\,CO\,\,\, (R)\, H_3B \leftarrow CO\,\,\,(S)\, [Mn(CO)_5]^-$