What is the correct definition of a mixture in physical science?

A mixture is defined as being composed of two or more substances, which can be elements or compounds, that are physically combined but not chemically altered. This means that the individual properties of each component remain unchanged and they retain their own characteristics. The correct definition emphasizes that a mixture can comprise various types of molecules and that these molecules do not undergo any chemical reactions to form new substances.

This characteristic of mixtures allows for various physical methods of separation, such as filtration or distillation, reflecting their unique properties. Unlike a pure substance, a mixture can vary in composition, making it flexible and diverse. This flexibility is distinct from homogeneous substances, which are uniform throughout, or from compounds, which consist of elements that are chemically bonded together in specific ratios.

The other choices don't accurately capture the essence of what a mixture is. For instance, the definition related to a homogeneous distribution describes a specific type of mixture but does not encompass all mixtures, particularly heterogeneous ones. The options suggesting that a mixture includes only one type of molecule or indicates that the substances within it are chemically combined both contradict the fundamental nature of what constitutes a mixture.