Carbon monoxide is mainly released into air by

Options

A. automobile exhaust
B. Incomplete combustion of coal
C. Incomplete combustion of firewood
D. All of the above

Answer

**Step-by-Step Solution:**

1. **Understanding Carbon Monoxide (CO):**
Carbon monoxide is a colorless, odorless gas that is harmful to human health. It is primarily produced from the incomplete combustion of carbon-containing fuels.

2. **Sources of Carbon Monoxide:**
The main sources of carbon monoxide emissions include:
- **Automobile Exhaust:** When fuels such as gasoline or diesel are burned in engines, incomplete combustion occurs, leading to the formation of carbon monoxide.
- **Incompletely Burned Fuels:** This includes coal and firewood. When these fuels are burned without enough oxygen, they produce carbon monoxide instead of carbon dioxide.

3. **Combustion Process:**
- **Complete Combustion:** In the presence of sufficient oxygen, carbon burns completely to produce carbon dioxide (CO2).
- **Incomplete Combustion:** When there is insufficient oxygen, carbon can form carbon monoxide (CO) instead of carbon dioxide.

4. **Conclusion:**
Based on the sources mentioned, carbon monoxide is mainly released into the air by:
- Automobile exhaust
- Incomplete combustion of coal
- Incomplete combustion of firewood

5. **Final Answer:**
Therefore, the correct answer is: **All of these.**

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