Final answer:
Normal rain is slightly acidic with a pH between 5 and 6 due to dissolved carbon dioxide that forms carbonic acid. Acid rain is more acidic with a pH less than 5 as it contains other dissolved compounds like sulfuric and nitric acids that lower the pH further.
Step-by-step explanation:
Normal rain is slightly acidic with a pH between 5 and 6, which means it is not pure water but has a mild level of acidity. This is primarily due to the presence of dissolved carbon dioxide from the atmosphere that reacts with the rainwater to form carbonic acid:
H₂O(l) + CO₂(g) → H₂CO₃(aq)
Acid rain, on the other hand, is rainwater with a pH of less than 5. It contains higher concentrations of acidic compounds, as nonmetal oxides such as CO2, SO2, SO3, NO, and NO₂ dissolve in the water, forming not just carbonic acid but also sulfuric and nitric acids, leading to an even lower pH level and more harmful environmental effects.