Which gas is primarily responsible for causing acid rain?

The gas primarily responsible for causing acid rain is sulfur dioxide. When sulfur dioxide is released into the atmosphere, typically from burning fossil fuels such as coal and oil, it can react with water vapor and other chemicals in the atmosphere to form sulfuric acid. This acidic transformation is a key process in the development of acid rain, which can lead to significant environmental issues such as damage to forests, soils, and aquatic ecosystems.

While other gases, such as nitrogen dioxide, can contribute to air pollution and related phenomena, they are not the primary drivers of acid rain. Nitrogen compounds may contribute to the formation of nitric acid in the atmosphere, but sulfur dioxide's ability to form strong acids upon interacting with atmospheric moisture makes it the leading cause of acid rain formation. Carbon dioxide, while it does contribute to a different form of acidification (like ocean acidification), is not a primary factor in acid rain. Ozone primarily acts as a pollutant in the lower atmosphere (troposphere) rather than contributing to acid rain. Therefore, the role of sulfur dioxide in the formation of acid rain is well established and is the reason it is identified as the correct answer.