9. Which type of air pollution can cause structural damage to buildings? acid rain chlorofluorocarbons fly ash dioxin

The type of air pollution that can cause structural damage to buildings is **acid rain**. ### Explanation: 1. **Acid Rain**: This occurs when sulfur dioxide (SO₂) and nitrogen oxides (NOₓ) are released into the atmosphere, where they react with water vapor, oxygen, and other chemicals to form sulfuric and nitric acids. When this acidic precipitation falls to the ground, it can corrode and damage buildings, especially those made of limestone, marble, and concrete. 2. **Chlorofluorocarbons (CFCs)**: These are primarily known for their role in ozone depletion rather than causing structural damage to buildings. 3. **Fly Ash**: This is a byproduct of burning coal in power plants and is often used in construction materials, but it does not directly cause structural damage. 4. **Dioxin**: This is a group of chemically-related compounds that are persistent environmental pollutants. While dioxins can have serious health effects, they are not known to cause structural damage to buildings. In summary, acid rain is the correct answer as it directly contributes to the deterioration of building materials.