Question

Given below are two statements:
Statement I: The pH of rain water is normally ~5.6.
Statement II: If the pH of rain water drops below 5.6, it is called acid rain.

• A. Both Statement I and Statement II are true.
• B. Both Statement I and Statement II are false.
• C. Statement I is true but Statement II is false.
  %
• D. Statement I is false but Statement II is true.

Hint:

A common misconception is that neutral rain should have a pH of 7. Remember that dissolved atmospheric CO₂ makes all natural rain slightly acidic, with a pH of about 5.6. Acid rain is defined as rain that is even more acidic than this baseline.

Answer 1

The Correct Option is A

To solve this question, we need to evaluate the given statements regarding the pH of rainwater and determine if they are true or false.

Understanding pH and Rainwater

The pH scale is used to measure the acidity or alkalinity of a solution. It ranges from 0 to 14, with 7 being neutral. A pH value less than 7 indicates acidity, whereas a value greater than 7 indicates alkalinity.

Statement I: The pH of rain water is normally ~5.6.

Normal rainwater is slightly acidic, typically with a pH of approximately 5.6. This is due to the natural presence of carbon dioxide (CO₂) in the atmosphere, which dissolves in rainwater to form carbonic acid, a weak acid. Therefore, under natural, unpolluted conditions, rainwater does have a pH around 5.6.

Statement II: If the pH of rain water drops below 5.6, it is called acid rain.

When the pH of rainwater falls below 5.6, it is considered to be more acidic than normal due to pollutants like sulfur dioxide (SO₂) and nitrogen oxides (NO_x) in the atmosphere. These pollutants can further react with water to create stronger acids, such as sulfuric acid and nitric acid, resulting in acid rain.

Conclusion

• Statement I is true because normal, unpolluted rainwater does indeed have a pH of about 5.6.
• Statement II is true because rain is termed "acid rain" when its pH drops below 5.6 due to increased acidic pollutants in the atmosphere.

Therefore, the correct answer is: Both Statement I and Statement II are true.