The oxide responsible for acid-rain is –

Question

Accepted Answer

The oxide responsible for acid rain is sulfur dioxide (SO₂), which is given as Option 3. Here is a detailed explanation supporting why SO₂ is the correct answer:

1. **Why SO₂ is Correct:**
   - Sulfur dioxide (SO₂) is a significant contributor to acid rain. When SO₂ is released into the atmosphere, it reacts with water vapor, oxygen, and other chemicals to form sulfuric acid (H₂SO₄). This acid then mixes with rainwater, resulting in acid rain. The process can be summarized by the following chemical reactions:
     - SO₂ + H₂O → H₂SO₃ (sulfurous acid)
     - 2SO₂ + O₂ → 2SO₃
     - SO₃ + H₂O → H₂SO₄ (sulfuric acid)
   - The presence of sulfuric acid in rainwater lowers the pH, making it acidic and harmful to the environment, aquatic life, and infrastructure.

2. **Why Other Options are Incorrect:**
   - **Option 1: H₂O (Water)**
     - Water itself is neutral and does not contribute to acid rain. It is the medium in which acidic compounds dissolve, but it is not responsible for the acidity.
   - **Option 2: CO (Carbon Monoxide)**
     - Carbon monoxide is a pollutant that affects air quality and human health but does not contribute to acid rain. It does not form acidic compounds in the atmosphere.
   - **Option 4: CO₂ (Carbon Dioxide)**
     - While carbon dioxide can dissolve in water to form carbonic acid (H₂CO₃), which is weakly acidic, it is not the primary cause of acid rain. The acidity from CO₂ is much less significant compared to that from sulfuric and nitric acids formed from SO₂ and NOx emissions.

In conclusion, sulfur dioxide (SO₂) is the primary oxide responsible for acid rain, making Option 3 the correct answer.