Which of the following alcohols is the least soluble in water ?

The general rule that explains solubility on the basis of the polarity of molecules is that “like dissolves like” In other words, polar compounds dissolve in polar solvents and nonpolar compounds dissolve in nonpolar solvents. This is generally true. because a polar solvent such as water has partial charges that can interact with the partial charges on-a polar compound. The negative poles of the solvent molecules surround the positive pole of the polar solute, and the positive poles of the solvent molecules surround the negative pole of the polar solute. Clustering of the solvent molecules around the solute molecules separates solute molecules from each other, which is what makes them soluble. The interaction between a solvent and a molecule or an ion that is dissolved in that solvent is called solvation
Because nonpolar compounds have no net charge, polar solvents are not attracted to them. In order for a nonpolar molecule to dissolve in a polar solvent such as water, the nonpolar molecule would have to push the water molecules apart,- disrupting their hydrogen bonding. Hydrogen bonding is so strong that it excludes the nonpolar compound. In contrast, nonpolar solutes dissolve in non-polar solvents because of the vander Waals interactions between solvent and solute molecules.

 

w.r.t. the question asked, l-pentanol has maximum number of carbons, so it is least soluble in water. {extent of H-bonding decreases}