Unpolluted rain water has a pH of:

Explanation

The correct answer is 5.6. Unpolluted rainwater is slightly acidic due to the formation of carbonic acid, which occurs when carbon dioxide in the atmosphere dissolves in rainwater. This process results in a pH of approximately 5.6. Option A (4.9) represents a more acidic condition that would not be typical for natural rainwater unless affected by additional pollutants. Option C (5.3) is closer but still more acidic than the average for unpolluted conditions. Finally, Option D (7.0) indicates a neutral pH, which does not account for the natural acidity introduced by carbonic acid.