Which of the following refrigerants is noted to have a low environmental impact?

HFC-134a is recognized for its relatively low impact on the environment compared to the other refrigerants listed. It has a lower ozone depletion potential (ODP) and a lower global warming potential (GWP) than CFC-12, which is a chlorofluorocarbon known for significant ozone depletion. While HCFC-22 also has some reduction in environmental impact compared to CFCs, it still contributes to ozone depletion, albeit at a lesser extent than CFC-12. R-410A, although widely used and considered more environmentally friendly than CFCs, has a higher GWP than HFC-134a.

Thus, HFC-134a is often a preferred choice in applications where minimizing environmental impact is a significant consideration, making it an appropriate answer to the question.