What is an emulsion?

An emulsion is defined as a mixture of two liquids that are not soluble in each other, which is precisely the assertion made in the selected answer. The most common type of emulsion involves oil and water, where the two components do not naturally mix. To achieve a stable emulsion, an emulsifying agent is typically used, which helps to disperse one liquid into the other, creating a stable blend. This process is essential in various applications, including food products, cosmetics, and pharmaceuticals, where the uniform distribution of ingredients is crucial for product effectiveness and stability.

In contrast, the other options describe different types of mixtures. For example, a mixture of two liquids that are soluble in each other would not result in an emulsion; instead, it would create a solution. Similarly, a solid mixed with a liquid refers to a suspension, and a gas mixed with a liquid could describe an aerated solution or foam, neither of which encapsulate the specific definition of an emulsion. Thus, the accurate understanding of emulsions as mixtures of immiscible liquids is key to grasping their role in various chemical and everyday contexts.