Final answer:
Chlorofluorocarbons (CFCs) have the highest ozone depletion potential among refrigerants, which is why they have been phased out under the Montreal Protocol in favor of HFCs and HCFCs that are less harmful to the ozone layer.
Step-by-step explanation:
The refrigerant type that has the highest ozone depletion potential is chlorofluorocarbons, commonly known as CFCs. These compounds, such as CCl₂F₂ (trichlorofluoromethane), have been widely used in refrigerants, air conditioning systems, foams, and aerosols. A single chlorine atom from CFCs can destroy ozone molecules for up to about two years before it is transported back to the surface. Due to their stability and long atmospheric lifetime, CFCs contribute to ozone depletion significantly. Following international concern over the destruction of the ozone layer, substances like CFCs have been phased out under the Montreal Protocol, a global agreement established in 1987. The most promising replacements for CFCs are hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons (HCFCs), which are considered to have a lesser impact on the ozone layer due to their structure, which allows them to break down more readily in the troposphere.