Which of the following refrigerants is prohibited for sale without EPA certification?

CFCs, or chlorofluorocarbons, are prohibited for sale and use without EPA certification due to their significant environmental impact, particularly their role in ozone depletion. These substances are known to contribute to the thinning of the ozone layer, which protects the Earth from harmful ultraviolet radiation.

As part of the Montreal Protocol, which aims to phase out substances that deplete the ozone layer, the sale and use of CFCs have been heavily restricted. Therefore, handling and purchasing these refrigerants legally requires specific certification regulated by the EPA. This ensures that only trained professionals are dealing with substances that can cause significant environmental harm if mismanaged.

In contrast, the other refrigerants listed, such as R-134a, R-410A, and R-404A, although regulated, do not carry the same prohibition on sale without certification as CFCs. While they may be subject to certain regulatory requirements, they do not pose the same level of environmental threat related to ozone depletion that CFCs do, making the certification requirement applicable specifically to CFCs in this context.