Final answer:
The Montreal Protocol phases out substances that deplete the ozone layer, including many CFCs and HCFCs. Refrigerants not called for a phase-out in the question are not specifically listed, but the protocol targeted CFCs and certain HCFCs while promoting alternatives like HFCs.
Step-by-step explanation:
Montreal Protocol and Refrigerants
The Montreal Protocol is an international agreement designed to phase out substances that deplete the ozone layer. Refrigerants such as chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) have been addressed within this protocol due to their high ozone-depleting potential.
Some substances, like carbon tetrachloride and methyl chloroform, are scheduled for phase-out under the protocol. However, the student's question implies looking for refrigerants that are not called for a phase-out under the Montreal Protocol, which specifically targets the phasing out of CFCs and certain HCFCs.
The agreement has led to the development of alternative refrigerants with less environmental impact, such as hydrofluorocarbons (HFCs). Although HFCs do not deplete the ozone layer, they are potent greenhouse gases and have their own environmental consequences. Despite this, the Montreal Protocol has been successful in reducing emissions of ozone-depleting substances, leading to signs of ozone layer recovery.