The natural source of acidity in rain water is carbonic acid sulfuric acid nitric acid all of the above

The natural source of acidity in rain water is all of the above. This is due to presence and abundance of carbon dioxide, nitrogen oxide, and sulfur dioxide in the atmosphere that can dissolve in rain water. Unpolluted rain water is made acidic due to CO2 and H2O in the air that forms carbonic acid. 

Nitrogen oxide is mainly present due to the nitrogen fixation caused by lightning, while sulfur dioxide is mainly present due to volcanic eruptions. Other sources such as human activity can also contribute to acid rain. 

Thermohaline circulation and gyres