Final answer:
An emulsion is a colloidal dispersion in which a hydrophobic liquid is dispersed in an aqueous solution, with examples including mayonnaise and milk. Emulsifying agents like soap and egg yolk are needed to stabilize emulsions.
Step-by-step explanation:
An emulsion is a colloidal dispersion where one liquid, which is hydrophobic, is dispersed in another, typically water or an aqueous solution, with which it is immiscible. Oil, fat, wax, and resin can all form emulsions with water, but the term "emulsion" most commonly refers to mixtures involving oil or fat. In the context of the choices provided in the question, options 1) and 2) are essentially the same since fats are a type of oil, which makes both a stable mixture of an aqueous liquid with oil and a stable mixture of an aqueous liquid with fat correct. However, soap, egg yolk, or other emulsifying agents are often required to stabilize these mixtures to prevent the two liquid phases from separating.
Common examples of emulsions include mayonnaise, which is oil in vinegar stabilized by egg yolk, and milk, which is an emulsion of butterfat in water stabilized by the protein casein. Other personal care products like lotions and creams are also classified as emulsions, which can either be oil-in-water or water-in-oil, depending on the product's needs and the desired effects on the skin.