The biggest source of acid rain is the oxide of:

Explanation

Acid rain results when sulfur dioxide (SO2) and nitrogen oxides (NOX) are emitted into the atmosphere and transported by wind and air currents.The biggest source of acid rain is the oxide of sulfur (S).Acid rain is formed when sulfur dioxide (SO2) and nitrogen oxides (NOx), primarily nitrogen (NO2), are released into the atmosphere as pollutants from various human activities, particularly the combustion of fossil fuels. These pollutants can undergo chemical reactions in the atmosphere and sulfuric acid (H2SO4) and nitric acid (HNO3), respectively. These acids can then combine with water vapor in the atmosphere and fall to the ground as acid rain.