Which of the following does NOT contribute to the increase of acidity in rainwater?

Rainwater acidity is primarily influenced by various pollutants that enter the atmosphere and subsequently dissolve in moisture. Carbon dioxide, sulfur dioxide, and even volcanic ash can increase the acidity of rainwater.

Carbon dioxide reacts with water to form carbonic acid, which is a weak acid that contributes to the overall pH reduction in rainwater. Sulfur dioxide, when released into the atmosphere, can react with oxygen and moisture to form sulfuric acid, which significantly lowers pH levels in precipitation and enhances its acidity. Volcanic ash can also contain sulfur compounds and other minerals that, when dispersed in the atmosphere, can lead to the formation of acids in rainwater.

In contrast, chlorofluorocarbons (CFCs) do not contribute to the acidity of rainwater. While CFCs are environmentally significant due to their role in ozone depletion, they do not have a direct chemical reaction with water that produces acidic compounds. They are stable molecules that do not easily react in the atmosphere to form acids, making them irrelevant when considering the factors that increase rainwater acidity.