Final answer:
A refrigerant cylinder with a gray body and a yellow top is designed to hold high-pressure refrigerants.
Step-by-step explanation:
The color code of a refrigerant cylinder is designed to provide information about the contents of the cylinder. In your question, a refrigerant cylinder with a gray body and a yellow top indicates it is designed to hold high-pressure refrigerants. So, the correct answer is (a) High-pressure refrigerants.
Refrigerants are substances used in cooling systems, such as air conditioners and refrigerators, to transfer heat. They undergo changes in state from liquid to gas and back to liquid as part of the refrigeration cycle. The containment of these substances in cylinders must adhere to safety regulations to prevent accidents, especially considering the high pressure under which some refrigerants are stored.