Which of the following refrigerants is considered ozone-depleting?

C. R-22 is considered ozone-depleting because it contains chlorine atoms, which are known to break down ozone in the stratosphere. Chlorofluorocarbons (CFCs) and hydro chlorofluorocarbons (HCFCs), such as R-22, release chlorine when they are broken down by ultraviolet (UV) radiation in the atmosphere. This chlorine can then catalyze the destruction of ozone molecules, which play a crucial role in blocking harmful UV radiation from reaching the Earth's surface.

In contrast, the other refrigerants mentioned, such as R-410A, R-134A, and R-404A, do not contain chlorine and are classified as more environmentally friendly alternatives. R-410A is a blend of hydrofluorocarbons (HFCs) which do not affect the ozone layer. Similarly, R-134A and R-404A are also HFCs and have been developed to replace older refrigerants while minimizing ozone depletion potential. The importance of this distinction lies in the environmental guidelines and regulations aimed at protecting the ozone layer, which has led to a gradual phase-out of ozone-depleting substances like R-22.