How is a mixture best defined?

A mixture is best defined as a combination of two or more substances that are not chemically bonded. This means that the components of a mixture retain their individual properties and can be separated by physical means, such as filtration or distillation. Unlike compounds—where elements are chemically bonded and lose their individual properties—a mixture allows each substance to maintain its unique characteristics.

In a mixture, the substances can be present in varying proportions, and their distribution can be heterogeneous (not uniform throughout) or homogeneous (uniform throughout), but the key point is that no chemical change occurs in the substances involved. This lack of chemical bonding is what differentiates a mixture from a compound.

Other definitions do not accurately describe mixtures: a combination of substances that are chemically bonded refers to a compound, while a substance with a uniform composition pertains more closely to a solution rather than a mixture. Lastly, a collection of pure substances does not capture the defining characteristic of mixtures, which is the combination without bonding.