Assertion : Acid rain causes lakes and rivers to become acidic .
Reason : Buildings materials like limestone, marble , etc. are weakened on reaction with acid rain.

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion.
B. If both assertion and reason are true but reason is not the c orrect explanation of assertion.
C. If assertion is true but reason is false.
D. If both assertion and reason are false.

Explanation

**Step-by-Step Solution:**

1. **Understanding Acid Rain:**
- Acid rain is defined as rainwater that has a pH of less than 5.6. Normal rainwater has a pH of about 5.6 due to the natural presence of carbonic acid formed from carbon dioxide in the atmosphere.
- Acid rain is primarily caused by the presence of sulfur dioxide (SO2) and nitrogen oxides (NOx) in the atmosphere, which can originate from industrial emissions, vehicle exhaust, and other sources.

2. **Formation of Acids in Rainwater:**
- When sulfur dioxide (SO2) reacts with oxygen (O2) in the atmosphere, it can form sulfuric acid (H2SO4) when it combines with water. This reaction decreases the pH of the rainwater.
- Similarly, nitrogen oxides (NO2) can react with water to form nitric acid (HNO3), which also contributes to the acidity of rainwater.

3. **Impact on Lakes and Rivers:**
- When acid rain falls into lakes and rivers, it mixes with the water and increases the concentration of hydrogen ions (H+), which lowers the pH of the water bodies, making them more acidic.
- This increase in acidity can harm aquatic life and disrupt ecosystems.

4. **Effect on Building Materials:**
- Acid rain can also react with building materials, particularly those containing calcium carbonate, such as limestone and marble.
- For example, when calcium carbonate (CaCO3) reacts with sulfuric acid (H2SO4), it produces calcium sulfate (CaSO4), carbon dioxide (CO2), and water (H2O). This reaction leads to the deterioration and weakening of these materials.

5. **Conclusion:**
- The assertion that "acid rain causes lakes and rivers to become acidic" is true.
- The reason that "building materials like limestone, marble, etc. are weakened on reaction with acid rain" is also true.
- However, the reason does not directly explain the assertion, as the assertion focuses on the impact of acid rain on water bodies, while the reason discusses the effect on building materials.

**Final Answer:**
Both the assertion and reason are true, but the reason does not correctly explain the assertion. Therefore, the correct option is B.

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