When coal burns in air ...... gas is mainly produced.

Options

A. `SO_2`
B. `NO_2`
C. `CO`
D. `CO_2`

Explanation

To answer the question "When coal burns in air, ...... gas is mainly produced," we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Composition of Coal**:
- Coal is primarily composed of carbon.

2. **Understand the Combustion Process**:
- When coal burns, it reacts with oxygen present in the air. This process is known as combustion.

3. **Chemical Reaction**:
- The combustion of carbon can be represented by the following chemical equation:
\[ \text{C (s) + O}_2 \text{(g) → CO}_2 \text{(g)} \]
- Here, carbon (C) combines with oxygen (O₂) to produce carbon dioxide (CO₂).

4. **Identify the Main Product**:
- From the combustion of coal, the main gas produced is carbon dioxide (CO₂).

5. **Conclusion**:
- Therefore, when coal burns in air, the gas that is mainly produced is carbon dioxide (CO₂).

### Final Answer:
When coal burns in air, carbon dioxide (CO₂) gas is mainly produced.

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