Which of the following is a common refrigerant used in HVAC systems?

R-410A is commonly used in HVAC systems due to its efficiency and environmental benefits. It is a hydrofluorocarbon (HFC) refrigerant that does not deplete the ozone layer and provides better cooling performance compared to older refrigerants. Its pressure characteristics and thermal properties make it suitable for use in air conditioning units and heat pumps, thereby contributing to energy savings and improved system performance.

In contrast, R-22 has been phased out in many places due to its ozone-depleting potential, and while R-134A is used more in refrigeration and automotive applications, it is not as prevalent in residential and commercial HVAC systems. Freon-11, another outmoded refrigerant, has also been largely discontinued due to its harmful environmental effects. Thus, the prevalence and regulatory favor towards R-410A make it the correct choice in this context.