Cosmetic preparations made by dissolving a solid, liquid, or gas into another substance are called?

The correct answer is solutions because a solution is a homogeneous mixture composed of a solute (the solid, liquid, or gas being dissolved) and a solvent (the substance in which the solute is dissolved). In the context of cosmetic preparations, solutions are often used to create serums, toners, and other types of liquid skincare products where the active ingredients are dissolved to ensure an even distribution and enhance effectiveness.

Suspensions, in contrast, are mixtures where solid particles are dispersed in a liquid but remain undissolved, often requiring shaking before use. Emulsions involve a mixture of two immiscible liquids, typically oil and water, stabilized by an emulsifying agent. Gels are semi-solid systems that contain a liquid component which is thickened or gelled, but they do not necessarily represent the straightforward dissolving process described in the question.

Thus, a solution is characterized by the complete dissolution of the solute in the solvent, making it the appropriate choice in this context.