What is one reason azeotropes cannot be fully separated through fractional distillation?

Azeotropes cannot be fully separated through fractional distillation primarily because they have a constant boiling point. This characteristic means that at a specific composition, the mixture of liquids will boil at a temperature that does not change, regardless of the ratios of the components in the mixture. As a result, when the azeotrope is heated, it vaporizes at this constant temperature and composition, allowing both components to evaporate together in the same ratio, which makes it impossible to achieve complete separation.

In contrast, the other options describe different phenomena that are not characteristic of all azeotropes. For instance, while some mixtures may evaporate simultaneously, not all mixtures behave this way during distillation. The formation of solids at certain temperatures applies to specific mixtures but is not a defining feature of azeotropes in general. Similarly, reactivity of components does not directly correlate with the formation of azeotropes or influence the ability to separate them via distillation. Hence, the defining factor of a constant boiling point is crucial in understanding why fractional distillation cannot achieve full separation of azeotropes.