Final answer:
The answer is option 3) oil. Oil is the substance that is insoluble in water, while salt, sugar, and vinegar are soluble in water.
Step-by-step explanation:
When we say a substance is insoluble, it means that it does not dissolve in water to form a homogeneous mixture or solution. Oil, such as vegetable oil or mineral oil, is a nonpolar substance. Water is a polar solvent. Because oil and water have different polarities, they do not mix. Instead, oil forms separate droplets or layers on top of water, leading to its insolubility.
On the other hand, salt, sugar, and vinegar are all soluble in water to some extent. Salt (NaCl) and sugar (sucrose) are both ionic compounds that can dissociate into ions when dissolved in water. Vinegar is a solution of acetic acid (CH3COOH) in water. The substance insoluble in water is oil. To explain using the rules of solubility, salt (NaCl) and sugar (C12H22O11) are soluble because they are ionic compounds and polar molecules, respectively, which water, a polar solvent, can readily dissolve. Vinegar, which mainly consists of acetic acid diluted in water, is also soluble. However, oil is a nonpolar molecule and does not dissolve in water, making it a heterogeneous mixture instead of a solution. This is because water molecules are not able to dissolve nonpolar substances effectively.