Which of the following substances is classified as a low-pressure refrigerant?

R-123 is classified as a low-pressure refrigerant primarily because of its pressure-temperature characteristics, which are lower compared to other refrigerants like R-12, R-134A, and R-22. Low-pressure refrigerants operate at lower pressures, which can make them suitable for certain applications, such as low-temperature refrigeration and specific commercial cooling systems.

R-123 is particularly used in large chiller systems and has a relatively low boiling point. Its low-pressure operation helps in minimizing the risk of leaks and other issues related to high-pressure systems, making it safer in many industrial applications. Understanding refrigerant classifications is essential for proper refrigeration system design, maintenance, and environmental considerations, as different refrigerants can have varying effects on system efficiency and environmental impact.