Which terminology best describes a substance that is not clearly mixed, such as in an emulsion?

The terminology that best describes a substance that is not clearly mixed, such as in an emulsion, is heterogeneous. In a heterogeneous mixture, the different components can be easily distinguished and are not uniformly distributed. This contrasts with homogeneous mixtures, where the composition is consistent throughout, making it difficult to identify individual components.

Emulsions, for example, consist of two immiscible liquids that are mixed together, such as oil and water. In this case, you can observe separate phases, which is characteristic of a heterogeneous mixture. The property of being heterogeneous allows for the elements within the mixture to remain distinct, as opposed to merging completely, which is crucial in understanding how emulsions function in cosmetic applications, such as creams and lotions.

The other terms listed do not accurately capture this concept; for instance, a colloidal mixture involves particles that are dispersed throughout another medium but may appear homogeneous at a glance. Soluble refers to the ability of a substance to dissolve in a solvent, which does not pertain to the mixing quality of an emulsion. Therefore, heterogeneous is the appropriate term for substances that, like emulsions, show clear separation between different components.