What are azeotropes in the context of mixtures?

Azeotropes are unique mixtures of two or more liquids that exhibit specific behavior when it comes to boiling and composition. The defining characteristic of an azeotrope is that it maintains a constant boiling point and composition during the phase transition from liquid to vapor. This means that when an azeotropic mixture is boiled, it will vaporize at a steady temperature and the vapor produced will have the same ratio of components as the liquid mixture, making it challenging to separate the individual components through simple distillation.

This property arises because the interactions between the molecules of the different components in an azeotropic mixture can cause deviations from the ideal behavior seen in many mixtures. Therefore, attempting to distill an azeotrope will not result in an enrichment of any one component, as it would for a typical mixture.

In contrast, the other options describe different characteristics of substances or mixtures. A pure substance would not fit the definition of an azeotrope, since azeotropes are inherently mixtures. Mixtures that can be easily separated by simple distillation would not have the constant boiling point and composition associated with azeotropes. Lastly, while varying densities and phases might describe certain mixtures, it does not capture the essence of how azeotropes behave in terms of their constant