Which of the following best defines a mixture?

A mixture is best defined as a homogeneous combination of two or more substances. This definition captures the essence of what a mixture is: it consists of multiple components that are combined physically rather than chemically, meaning that the individual substances retain their properties and can typically be separated by physical means.

In a homogeneous mixture, the components are evenly distributed throughout, so you cannot easily distinguish one substance from another. An example of this is saltwater, where the salt is dissolved uniformly in water.

The other options do not accurately describe mixtures. For instance, a mixture is not limited to solvents only or restricted to solids; it can involve gases and liquids as well. Furthermore, the notion of a definite composition applies to compounds rather than mixtures, as mixtures can vary in proportion and still remain mixtures. This flexibility in composition is a key characteristic that distinguishes mixtures from pure substances.