Introduction:
Acid rain refers to the precipitation that contains high levels of acids, primarily sulfuric acid and nitric acid, formed through the reaction of water vapor with sulfur dioxide (SO2) and nitrogen oxides (NOx) in the atmosphere. The pH scale is used to measure the acidity or alkalinity of a substance, and it ranges from 0 to 14, with 7 being neutral, values below 7 being acidic, and values above 7 being alkaline. Acid rain typically has a pH value below 5.6, indicating its acidic nature.

Explanation:
The correct answer is option 'A' - the pH of acid rain should always be less than 5.6 even after precipitation. This is because acid rain is formed when pollutants such as sulfur dioxide and nitrogen oxides are released into the atmosphere by human activities such as burning fossil fuels and industrial processes. These pollutants undergo chemical reactions with water vapor in the atmosphere to form sulfuric acid and nitric acid, which then combine with rainwater to form acid rain.

Effects of Acid Rain:
Acid rain can have detrimental effects on the environment, including:

1. Damage to Plants and Trees: Acid rain can damage plants and trees by damaging their leaves, inhibiting their growth, and reducing their ability to photosynthesize. This can lead to decreased crop yields and the death of forests.

2. Harm to Aquatic Life: Acid rain can lower the pH of lakes, rivers, and streams, making them more acidic. This can be harmful to aquatic organisms such as fish, amphibians, and invertebrates, as they are sensitive to changes in pH levels.

3. Corrosion of Buildings and Infrastructure: Acid rain can corrode buildings, bridges, and other infrastructure made of materials such as limestone, marble, and metal. This can result in structural damage and the need for costly repairs.

Importance of pH:
The pH level of a substance determines its acidity or alkalinity. A pH value below 7 indicates acidity, while a pH value above 7 indicates alkalinity. The pH scale is logarithmic, meaning that each unit represents a tenfold difference in acidity or alkalinity. For example, a substance with a pH of 4 is ten times more acidic than a substance with a pH of 5.

Reason for pH of Acid Rain Being Less Than 5.6:
The pH of acid rain is typically below 5.6 because it contains high levels of sulfuric acid and nitric acid. These acids are formed when sulfur dioxide and nitrogen oxides react with water vapor in the atmosphere. The resulting acids then combine with rainwater, lowering its pH and making it acidic.

Conclusion:
In conclusion, the pH of acid rain should always be less than 5.6 even after precipitation. Acid rain is formed when pollutants react with water vapor in the atmosphere, resulting in the formation of sulfuric acid and nitric acid. These acids then combine with rainwater, making it acidic. Acid rain can have detrimental effects on the environment, including damage to plants and trees, harm to aquatic life, and corrosion of buildings and infrastructure. Monitoring and reducing the emissions of pollutants that contribute to acid rain is crucial for mitigating its impacts.