The main contributor of acid rain is :

Options

A. `H_2SO_4`
B. `CaCO_3`
C. `CH_3COOH`
D. `PAN`.

Answer

To determine the main contributor of acid rain, we need to analyze the components that lead to the formation of acid rain.

### Step-by-Step Solution:

1. **Understanding Acid Rain**:
Acid rain is primarily caused by the presence of sulfuric acid (H2SO4) and nitric acid (HNO3) in the atmosphere. These acids are formed from the oxidation of sulfur dioxide (SO2) and nitrogen oxides (NOx).

2. **Formation of Sulfuric Acid**:
- Sulfur dioxide (SO2) is released into the atmosphere from sources such as volcanic eruptions and burning fossil fuels.
- SO2 reacts with oxygen (O2) in the presence of water (H2O) to form sulfuric acid (H2SO4).
- The reaction can be summarized as:
\[ \text{SO}_2 + \text{O}_2 + \text{H}_2\text{O} \rightarrow \text{H}_2\text{SO}_4 \]

3. **Formation of Nitric Acid**:
- Nitrogen oxides (NOx), particularly nitrogen dioxide (NO2), are also released into the atmosphere from vehicle emissions and industrial processes.
- NO2 reacts with oxygen and water to form nitric acid (HNO3).
- The reaction can be summarized as:
\[ \text{NO}_2 + \text{O}_2 + \text{H}_2\text{O} \rightarrow \text{HNO}_3 \]

4. **Identifying the Main Contributors**:
- The two major acids responsible for acid rain are H2SO4 and HNO3. Among these, sulfuric acid (H2SO4) is often considered the main contributor due to its higher concentration in acid rain.

5. **Evaluating the Options**:
- The options provided are:
- A) H2SO4
- B) CaCO3
- C) CH3COOH (Acetic Acid)
- D) Pan (not a chemical relevant to acid rain)
- From the analysis, H2SO4 is indeed a major component of acid rain, while the other options do not contribute to acid rain formation.

### Conclusion:
The main contributor of acid rain is **H2SO4** (sulfuric acid).