Which of the following is a characteristic of pure substances?

A pure substance is defined by its consistent and uniform composition throughout. One of the key characteristics of pure substances is that they have specific, well-defined melting and boiling points. This means that when a pure substance is heated, it will transition from solid to liquid at a specific temperature (melting point) and from liquid to gas at another specific temperature (boiling point), regardless of the amount of the substance present.

In contrast, mixtures exhibit varying physical properties because they contain different components that can have their own melting and boiling points. As a result, the melting and boiling points of a mixture can depend on the proportion of each component, which leads to a range of temperatures rather than specific values.

Therefore, the characteristic of having defined melting and boiling points highlights the homogeneity and consistent identity of pure substances, distinguishing them from mixtures.