What is meant by the term mixture?

The term "mixture" refers to a system where two or more different substances are present in the same space but do not undergo any chemical combination. In a mixture, each substance retains its individual properties, which is a crucial characteristic that distinguishes it from a compound, where substances are chemically bonded.

For instance, when salt and sand are mixed together, both materials can be easily separated, and each retains its original properties. This characteristic also implies that the proportions of the substances in a mixture can vary.

In contrast, other options describe scenarios that involve chemical reactions or compounds rather than mixtures. A is incorrect because it describes substances that are chemically combined, which refers to a compound rather than a mixture. C describes a compound, which results from a chemical reaction where elements combine. D suggests a reaction scenario where substances react with each other, which again does not align with the definition of a mixture. Thus, the only choice that accurately represents the concept of a mixture is that of different substances in the same space but not chemically joined together.