For acid rain, the pH of rain water should be less than

Normal rainwater is slightly acidic with a pH of about 5.6 due to the natural absorption of atmospheric CO₂, which forms weak carbonic acid (H₂CO₃). When the pH of rainwater falls below 5.6, it is classified as acid rain. Acid rain occurs primarily due to the dissolution of sulfur oxides (SO₂, SO₃) and nitrogen oxides (NOₓ) in atmospheric moisture, forming sulfuric acid (H₂SO₄) and nitric acid (HNO₃). These pollutants are mainly emitted from industrial activities, vehicle exhaust, and burning of fossil fuels.