What is considered acid rain?

• A. Precipitation with a pH above 7
• B. Precipitation with a pH between 5.2 and 5.6
• C. Precipitation with a pH lower than 5.2
• D. Precipitation with barely detectable acid elements

Answer: (C)

Acid rain is defined as precipitation that has a pH level lower than 5.6, primarily due to the presence of sulfuric and nitric acids formed from atmospheric pollutants. When these acids mix with moisture in the atmosphere, they can significantly lower the pH of rainwater, leading to a pH below 5.6. The threshold of 5.6 is often used as a standard because it represents the natural acidity of unpolluted rainwater, which is slightly acidic due to the presence of carbon dioxide in the atmosphere. Since option C specifies precipitation with a pH lower than 5.2, it accurately captures the essence of what constitutes acid rain. This lower pH indicates a more significant concentration of acid in the rain, which can have harmful effects on the environment, including damage to aquatic ecosystems, soil degradation, and deterioration of buildings and monuments.