Final answer:
The synthetic substitute currently used with blends containing HCFCs is HFC-134a (A), a hydrofluorocarbon that does not deplete the ozone layer, used to replace compounds like Freon-12 in refrigeration systems.
Step-by-step explanation:
The synthetic substitute currently used with blends containing HCFCs is HFC-134a (A). Hydrofluorocarbons (HFCs) are compounds that have been used to replace chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) in various applications, particularly as refrigerants. Compounds like HFC-134a do not contain chlorine, which was a key component responsible for ozone depletion from the previously used CFCs and HCFCs.
HFC-134a, or 1,1,1,2-tetrafluoroethane, is a non-ozone depleting gas that is now widely used in refrigeration systems, replacing substances such as Freon-12 (R-12 or CFC-12). Its use became more widespread after the international environmental legislation under the Montreal Protocol mandated the phasing out of CFCs due to their harmful effects on the ozone layer.