Which substance is necessary to bind oil and water together?

The correct answer is emulsifiers because they serve the specific function of allowing oil and water to mix together, which typically do not blend due to their differing polarities. Emulsifiers contain both a hydrophilic (water-attracting) part and a hydrophobic (water-repelling) part, allowing them to interact with both oil and water molecules. This dual nature enables them to stabilize a mixture of oil and water, creating what is known as an emulsion.

In various applications, emulsifiers can be found in food products like mayonnaise, cosmetics, and pharmaceuticals, where they help to create a uniform mixture that doesn't separate. Their ability to maintain stability in these mixtures is essential in preventing the separation of the components over time.

Other choices such as thickeners, solvents, and surfactants, while related to mixtures and solutions in different ways, do not serve the primary purpose of binding oil and water together in the same effective manner as emulsifiers do. Thickeners primarily alter the viscosity of a liquid, solvents are used to dissolve other substances, and surfactants reduce surface tension but do not necessarily create a stable mixture of oil and water.