Acid rain will occur when the pH of rain water is less than ________.

Acid rain refers to rainfall with a pH less than 5.6, making it more acidic than normal rainwater. Under natural conditions, pure rainwater is slightly acidic, with a pH of around 5.6 due to the presence of dissolved carbon dioxide forming weak carbonic acid. However, when harmful gases like sulfur dioxide (SO2) and nitrogen oxides (NO2) are released into the atmosphere—mostly from the burning of fossil fuels—they react with water vapor to form stronger acids such as sulfuric acid (H2SO4) and nitric acid (HNO3).