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

The correct answer is:
$CO>H_{2}O>F^{-}>S^{2-}$

Explanation:
The strength of ligands is determined by the spectrochemical series, which is an experimentally determined order of ligand field strengths based on the crystal field splitting energy (${\Delta }_o$) they produce in coordination complexes.

The spectrochemical series arranged in order of increasing field strength (from weak field to strong field ligands) is:
$I^{-}<{\mathrm{Br}}^{-}<S^{2-}<{\mathrm{SCN}}^{-}<{\mathrm{Cl}}^{-}<N^{3_{-}}<F^{-}<{\mathrm{OH}}^{-}<C_2{O_4}^{2-}<H_{2}O<{\mathrm{NCS}}^{-}<{\mathrm{EDTA}}^{4-}<{\mathrm{NH}}_3<\mathrm{en}<{\mathrm{CN}}^{-}<\mathrm{CO}$

To arrange the given ligands in order of decreasing field strength, we reverse their order in the spectrochemical series:
1. Carbon monoxide ($CO$) is a strong field, $\pi$-acid ligand and has the highest field strength among the options.
2. Water ($H_{2}O$) is a neutral oxygen donor ligand, behaving as a weak-to-intermediate field ligand.
3. Fluoride ($F^{-}$) is a weak field halide ligand.
4. Sulfide ($S^{2-}$) is a very weak field donor and lies near the beginning of the series, having the lowest field strength of the group.

Therefore, the decreasing order of field strength is:
$CO>H_{2}O>F^{-}>S^{2-}$