Which of the following refrigerants has the designation R-40?

The refrigerant designated as R-40 is actually methyl chloride. In the context of refrigerants, R-40 refers specifically to the compound that serves as a refrigerant in various applications. Methyl chloride is known for its efficiency and effectiveness in refrigeration systems, and it has distinct thermodynamic properties that make it suitable for cooling processes.

The other options do not correspond to the designation R-40: Freon 12 is known as R-12, ammonia is designated as R-717 and is widely used in industrial refrigeration, while carbon dioxide is referred to as R-744. Each of these refrigerants has different characteristics and applications, which is important for understanding their individual uses in the industry.