The answer is a) oil.
Water is a polar solvent, meaning it has a partial positive charge on one side and a partial negative charge on the other. This property allows it to effectively dissolve other polar substances. Salt (sodium chloride) and sugar (sucrose) both contain ionic or polar covalent bonds, which interact well with water molecules, allowing them to dissolve easily. Ethanol, while not as polar as water, has a hydroxyl (-OH) group that can engage in hydrogen bonding with water, which also facilitates its dissolution.
In contrast, oil is nonpolar and does not have an affinity for polar solvents like water. This is why oil and water do not mix; the molecules of oil do not interact with water in a way that would allow them to dissolve. Therefore, among the options provided, oil is the least likely to dissolve in water.