* Solubility: Solubility is the ability of a substance (solute) to dissolve in another substance (solvent). Substances dissolve when the forces of attraction between the solute and solvent molecules are stronger than the forces holding the solute molecules together.

* Polar vs. Nonpolar: Salt (sodium chloride) is an ionic compound, meaning it's composed of charged particles (ions). It's highly polar, meaning it has a positive and negative end. Baby oil is a nonpolar substance, meaning it has no distinct positive or negative ends.

* "Like Dissolves Like": A general rule in chemistry is "like dissolves like." This means polar substances tend to dissolve in other polar substances, and nonpolar substances dissolve in nonpolar substances.

Because salt is polar and baby oil is nonpolar, they don't mix well. The forces of attraction between the salt ions are stronger than the forces between the salt ions and the baby oil molecules. As a result, the salt will not dissolve in the baby oil.