Which of the following is a restriction related to the sale of refrigerant containers?

The correct answer highlights an essential regulation regarding the sale of refrigerants, which specifically necessitates that refrigerant containers are only sold to certified individuals. This requirement is part of the efforts to ensure that only those who have completed necessary training and obtained the appropriate certification handle potentially harmful substances like refrigerants.

The certification demonstrates that the individual has a proper understanding of the regulations, safe handling, and environmental considerations inherent in using and disposing of refrigerants. This restriction helps prevent misuse, accidental release, and environmental damage, promoting responsible behavior among those working with refrigerants.

In contrast, while a licensed contractor may have the necessary credentials to handle refrigerants, it does not encompass all individuals that may need to buy refrigerants. Similarly, warning labels can be key for safety, and size restrictions might exist for certain regulations, but the fundamental focus of this question lies in ensuring that only individuals who are certified are permitted to purchase refrigerants, as that reflects the broader intent of the laws surrounding refrigerant management and environmental protection.