Which of following pH value represents acidic rainwater?

pH < 5.6

The correct answer is option 3. pH < 5.6.

Acid rain is a type of precipitation that has an unusually low pH, making it acidic. The acidity of rainwater is primarily caused by the presence of pollutants such as sulfur dioxide (\(SO_2\)) and nitrogen oxides (\(NO_x\)) in the atmosphere. These pollutants are released into the air through human activities such as burning fossil fuels (coal, oil, and natural gas) for energy production, industrial processes, and transportation.

When \(SO_2\) and \(NO_x\) are released into the atmosphere, they can undergo chemical reactions with water vapor, oxygen, and other atmospheric components to form sulfuric acid (\(H_2SO_4\)) and nitric acid (\(HNO_3\)), respectively. These acids dissolve in water droplets in the atmosphere, forming acidic solutions.

When rain falls through the atmosphere containing these acidic pollutants, it combines with the acidic solutions, leading to the formation of acidic rainwater. The pH of normal, unpolluted rainwater is around 5.6 due to the presence of dissolved carbon dioxide, which forms carbonic acid (\(H_2CO_3\)). However, acid rain can have a pH value much lower than 5.6, often ranging from 4 to 5 or even lower in severely affected areas.

The acidity of acid rain can have detrimental effects on the environment, including:

1. Damage to vegetation: Acid rain can damage leaves, inhibit plant growth, and leach nutrients from the soil, leading to reduced crop yields and forest decline.

2. Harm to aquatic ecosystems: Acid rain can acidify lakes, rivers, and streams, affecting aquatic life such as fish, amphibians, and aquatic plants. It can also disrupt the reproductive cycles of aquatic organisms and degrade habitats.

3. Corrosion of buildings and infrastructure: Acid rain can corrode metals, degrade building materials (such as limestone and marble), and damage monuments and structures made of concrete or metal.

In summary, acidic rainwater typically has a pH value below 5.6 due to the presence of sulfuric acid and nitric acid formed from atmospheric pollutants. These acids can have widespread environmental impacts, making acid rain a significant environmental concern.