An emulsion consists of which two substances?

An emulsion is a type of colloidal system where one liquid is dispersed in another immiscible liquid, typically involving oil and water. This dispersion allows for the oil droplets to remain suspended throughout the water phase, resulting in a stable mixture. The process of emulsification often requires an emulsifying agent or surfactant to stabilize the mixture and prevent the two liquids from separating.

In this context, the combination of oil and water forms the classic example of an emulsion, such as mayonnaise or salad dressings, where the oil is dispersed in an aqueous phase. The other options do not represent an emulsion; for example, alcohol and water form a homogeneous solution rather than a dispersed mixture; sugar dissolves in water creating a solution rather than a distinct emulsion; and air and liquid can result in foams or aerosols, but not in an emulsion format. Therefore, the correct pairing of substances that forms an emulsion is oil and water.