Which of the following is correct order of ligand field strength?
$\mathrm{S}^{2-}<\mathrm{C}_{2} \mathrm{O}_{4}^{2-}<\mathrm{NH}_{3} < $ en $<\mathrm{CO}$
$\mathrm{CO}<\mathrm{en}<\mathrm{NH}_{3}<\mathrm{C}_{2} \mathrm{O}_{4}^{2}<\mathrm{S}^{2-}$
$\mathrm{S}^{2-}<\mathrm{NH}_{3}<$ en $<\mathrm{CO}<\mathrm{C}_{2} \mathrm{O}_{4}^{2}$
$\mathrm{NH}_{3}<\mathrm{en}<\mathrm{CO}<\mathrm{S}^{2-}<\mathrm{C}_{2} \mathrm{O}_{4}^{2}$
