The compound FeS, or iron(II) sulfide, is generally considered insoluble in water. This means that it does not dissolve well when mixed with water, and instead tends to remain as a solid.
One key reason for this insolubility is the nature of ionic compounds. Iron(II) sulfide is made up of iron ions (Fe2+) and sulfide ions (S2-). When these ions attempt to separate in water, they are held together by strong ionic bonds, which are not easily overcome by the interactions with water molecules. As a result, FeS does not break apart into its ionic components in a significant way.
Moreover, the solubility of compounds in water is influenced by factors such as temperature and the presence of other ions in the solution. In the case of FeS, even under varying conditions, it remains predominantly insoluble due to its strong crystal lattice structure and the low tendency of the individual ions to interact favorably with water.