The correct sequence of ligands in the order of decreasing field strength is :

Explanation

Ligand Field Strength

• The field strength of ligands is determined by their ability to split the d-orbitals of a central metal ion in a coordination complex.
• This is often described using the spectrochemical series, which arranges ligands in order of their field strength.
• Stronger field ligands cause greater splitting of the d-orbitals, leading to higher energy differences between the d-orbital sets.
• Common order of field strength for some ligands is:
  • ( \(CO > CN^- > NO_2^- > en > NH_3 > NCS^- > H_2O > EDTA^{4-} > OH^- > F^- > S^{2-} \))

Conclusion

Based on the given options and the general spectrochemical series, the correct sequence in decreasing order of field strength is CO > H2O > F- > S2-