The correct option is **D. NO\(_{2}\)**. ### Detailed Explanation: **What is Acid Rain?** Acid rain refers to any form of precipitation (rain, snow, sleet, or hail) that has a higher acidity than normal, typically with a pH of less than 5.6. This increased acidity is primarily due to the presence of sulfuric acid (H\(_2\)SO\(_4\)) and nitric acid (HNO\(_3\)), which are formed when certain oxides react with water in the atmosphere. **How Does NO\(_2\) Contribute to Acid Rain?** 1. **Formation of Nitric Acid:** - Nitrogen dioxide (NO\(_2\)) is a significant pollutant that can be produced from vehicle emissions and industrial processes. - In the atmosphere, NO\(_2\) can react with water (H\(_2\)O) to form nitric acid (HNO\(_3\)): \[ 3 \text{NO}_2 + \text{H}_2\text{O} \rightarrow 2 \text{HNO}_3 + \text{NO} \] - This reaction shows that NO\(_2\) contributes directly to the formation of acid rain by producing nitric acid, which lowers the pH of precipitation. 2. **Environmental Impact:** - Acid rain can have harmful effects on ecosystems, including soil degradation, water body acidification, and damage to plant life and aquatic organisms. ### Why the Other Options Are Incorrect: **A. CO (Carbon Monoxide):** - Carbon monoxide (CO) is a colorless, odorless gas that is primarily produced from incomplete combustion of fossil fuels. - While CO can contribute to air pollution and has health effects, it does not form acids in the atmosphere and therefore does not contribute to acid rain. **B. NO (Nitric Oxide):** - Nitric oxide (NO) is another nitrogen oxide that can be produced from combustion processes. - While it can react to form NO\(_2\) in the atmosphere, it does not directly contribute to acid rain. It is the NO\(_2\) that ultimately leads to the formation of nitric acid. **C. H\(_{2}\)O\(_{2\) (Hydrogen Peroxide):** - Hydrogen peroxide is a strong oxidizing agent and can be found in the atmosphere, but it does not contribute to acid rain. - It can participate in various chemical reactions, but it does not lead to the formation of significant acids like sulfuric or nitric acid in the context of acid rain. ### Summary of Key Points: - **Acid Rain Formation:** Acid rain is primarily caused by sulfuric and nitric acids formed from oxides. - **Role of NO\(_2\):** Nitrogen dioxide (NO\(_2\)) reacts with water to form nitric acid, contributing to acid rain. - **Other Options:** CO, NO, and H\(_2\)O\(_2\) do not contribute to acid rain formation. - **Environmental Impact:** Acid rain can harm ecosystems, affecting soil, water bodies, and living organisms. ### Revision Summary: - Acid rain is caused by sulfuric and nitric acids. - NO\(_2\) is a key contributor to acid rain through the formation of nitric acid. - CO, NO, and H\(_2\)O\(_2\) do not contribute to acid rain. - Understanding the chemical reactions involved is crucial for grasping the concept of acid rain.