The correct answer is C. 5.
A pH value of 7 is considered neutral. A pH value below 7 is considered acidic, and a pH value above 7 is considered basic. The pH scale is logarithmic, so a pH value of 5 is 10 times more acidic than a pH value of 6.
Rainwater is naturally slightly acidic due to the presence of carbon dioxide in the atmosphere. When carbon dioxide dissolves in water, it forms carbonic acid. However, human activities, such as burning fossil fuels, can release additional pollutants into the atmosphere, which can make rainwater more acidic.
Acidic rain can have a number of negative effects on the environment. It can corrode metals, damage buildings and infrastructure, and harm plants and animals. It can also leach pollutants from the soil into water bodies, which can contaminate drinking water and harm aquatic life.
There are a number of things that can be done to reduce the acidity of rainwater. One is to reduce emissions of pollutants into the atmosphere. Another is to plant trees, which can absorb carbon dioxide from the atmosphere.