Which statement is true about mixtures in refrigeration?

The statement that mixtures in refrigeration maintain separate existence regardless of how well they are blended is correct. In the context of refrigeration systems, a mixture refers to a combination of two or more components, such as different refrigerant gases or a refrigerant and oil. Even when these components are blended together, they can still exist in distinct phases. For example, a mixture of refrigerants may not fully dissolve into a single homogeneous phase at certain conditions of temperature and pressure. This behavior is important because it influences how the mixture operates within the refrigeration system, including its thermodynamic properties and efficiency.

In contrast, the other options do not accurately describe mixtures. Mixtures do not have fixed proportions of their components; they can vary depending on the system's needs and operational conditions. Additionally, mixtures can consist of both liquid and gaseous refrigerants, not limited to just gaseous types. Lastly, mixtures are not restricted to being made up solely of refrigerants; they can also include other substances, such as lubricating oils or additives that enhance performance. Understanding these characteristics is crucial for effectively working with refrigerants and maintaining safe and efficient refrigeration systems.