Acid Rain Causes River Acidification

Steps:

• Identify the problem: Rivers becoming more acidic means increased H+ ions from external sources.
• Link to environmental causes: Acidification often results from atmospheric pollutants forming weak acids in water.
• Evaluate options: Match each to known pollution effects on water pH.
• Select best fit: Choose the direct cause of acid deposition in rivers.

Why A is correct:

• Sulfur dioxide (SO2) from air pollution reacts with water vapor to form sulfuric acid (H2SO4), which falls as acid rain and lowers river pH, per acid rain chemistry.

Why the others are wrong:

• B: Deforestation increases erosion and sedimentation but does not directly acidify water.
• C: Insecticides are toxic but primarily cause biological harm, not pH changes.
• D: Nitrate fertilizers cause eutrophication and algal blooms, raising pH via photosynthesis, not lowering it.

Final answer: A