To determine the amount of acid rain that might occur in the hydrologic cycle of an area, the most relevant option would be:
D. A device that measures the amount of chemicals released into the air by a factory.
This is because the primary contributors to acid rain are sulfur dioxide (SO₂) and nitrogen oxides (NOₓ), which are pollutants released into the atmosphere by industrial activities, vehicles, and other sources. Measuring the emissions of these chemicals would provide insight into the potential for acid rain formation in the area.