Explanation: Acid rain is a form of precipitation that has a lower pH than normal rain, typically caused by the release of sulfur dioxide (SO2) and nitrogen oxides (NOx) into the atmosphere. These gases react with water, oxygen, and other chemicals in the atmosphere to form acids, which then fall to the ground as rain, snow, or fog. The primary cause of acid rain is the emission of sulfur dioxide (SO2) and nitrogen oxides (NOx) from industrial processes, particularly the burning of fossil fuels such as coal and oil.
Sulfur dioxide (SO2) is a major contributor to acid rain due to its widespread presence in industrial emissions. When SO2 is released into the atmosphere, it undergoes a series of chemical reactions. First, it reacts with water (H2O) and oxygen (O2) to form sulfur trioxide (SO3). This reaction can be represented as:
\[ \text{SO}_2 + \frac{1}{2} \text{O}_2 \rightarrow \text{SO}_3 \]
Sulfur trioxide then reacts with water to form sulfuric acid (H2SO4):
\[ \text{SO}_3 + \text{H}_2\text{O} \rightarrow \text{H}_2\text{SO}_4 \]
Sulfuric acid is a strong acid and is a major component of acid rain. When it falls to the ground, it can have harmful effects on the environment, including damage to forests, lakes, and buildings.
Nitrogen oxides (NOx) also contribute to acid rain. They are produced by high-temperature combustion processes, such as those occurring in vehicle engines and power plants. Nitrogen oxides can react with water, oxygen, and other chemicals in the atmosphere to form nitric acid (HNO3):
\[ \text{NO}_2 + \text{H}_2\text{O} \rightarrow \text{HNO}_3 + \text{HNO}_2 \]
Nitric acid is another component of acid rain and can also cause environmental damage.
Carbon dioxide (CO2) and carbon monoxide (CO) do not directly cause acid rain. CO2 is a greenhouse gas that contributes to global warming and climate change, but it does not form acids in the atmosphere in significant amounts. CO is a toxic gas produced by incomplete combustion of carbon-containing fuels and does not react with water or oxygen to form acids.
Methane (CH4) is a potent greenhouse gas that contributes to global warming, but it does not directly cause acid rain. Methane does not react with water or oxygen in the atmosphere to form acids.
In summary, sulfur dioxide (SO2) is the correct answer because it is a major contributor to acid rain due to its ability to react with water and oxygen in the atmosphere to form sulfuric acid, which falls to the ground as acid rain.