What kind of acid contributes to the slight acidity of normal rain?

Normal rain is slightly acidic, typically with a pH ranging from 5.0 to 5.6, due to the presence of carbon dioxide in the atmosphere. When carbon dioxide dissolves in rainwater, it reacts to form carbonic acid. This natural process is part of the carbon cycle; as plants respire and produce carbon dioxide, it mixes with atmospheric moisture, leading to the formation of this weak acid.

While the other acids mentioned can also contribute to acid rain, they are primarily associated with human-made pollution. Sulfuric acid, for instance, arises from the combustion of fossil fuels, and nitric acid comes from vehicle emissions and industrial activities. Acetic acid, found in vinegar, does not significantly play a role in the acidity of rainwater. Consequently, carbonic acid is the primary agent responsible for the natural acidity observed in normal rain.