An azeotrope is a mixture of two or more liquids that boils at a constant temperature and composition, meaning that the liquid mixture has the same composition in both the liquid and vapor phases. In other words, when an azeotropic mixture is heated, the vapor that is produced has the same composition as the liquid mixture.

Explanation:
- An azeotrope is a mixture of refrigerants without phase separation (Option C). This means that the refrigerants in the mixture do not separate into different phases (such as liquid and vapor) when heated or cooled.
- Azeotropes are often used in refrigeration systems because they have specific properties that make them ideal for certain applications. For example, some azeotropes have a lower boiling point than the individual refrigerants, allowing for more efficient cooling.
- Azeotropes can also be used to achieve a desired vapor pressure-temperature relationship in a refrigeration system. By selecting the appropriate azeotrope, the desired temperature range for cooling can be achieved.
- Azeotropes can be made up of different combinations of refrigerants, depending on the specific application. Some common examples of azeotropes used in refrigeration systems include R-410A and R-404A.
- It is important to note that azeotropes are not limited to refrigerants. They can also be found in other mixtures of liquids, such as ethanol and water.
- Azeotropes can be challenging to separate into their individual components because of their constant boiling point and composition. However, there are techniques available, such as distillation, that can be used to separate azeotropic mixtures if necessary.