Combustion of which of the following fuels requires the highest amount of excess air :

Options

A. light diesel oil (LDO)
B. natural gas
C. LPG
D. coal

Explanation

**Step-by-Step Solution:**

1. **Understanding Combustion**: Combustion is a chemical reaction where a fuel reacts with oxygen to produce heat and light. The amount of air (oxygen) required for complete combustion can vary depending on the type of fuel.

2. **Identifying the Fuels**: The question provides four types of fuels:
- Light Diesel Oil (liquid)
- Natural Gas (gas)
- LPG (liquid petroleum gas)
- Coal (solid)

3. **Analyzing Each Fuel**:
- **Light Diesel Oil**: Being a liquid fuel, it generally requires less excess air for combustion compared to solid fuels.
- **Natural Gas**: This is a gaseous fuel and also requires a moderate amount of air for combustion.
- **LPG**: Similar to natural gas, LPG is in liquid form but vaporizes during combustion. It also requires a moderate amount of air.
- **Coal**: Coal is a solid fuel and typically requires a higher amount of excess air for combustion due to its structure and the nature of the combustion process.

4. **Comparing Air Requirements**: When comparing the combustion of these fuels:
- Liquid fuels (like Light Diesel Oil) require less excess air.
- Gaseous fuels (Natural Gas and LPG) require a moderate amount of excess air.
- Solid fuels (like Coal) require the highest amount of excess air due to the need for complete combustion of the solid particles.

5. **Conclusion**: Based on the analysis, the fuel that requires the highest amount of excess air for combustion is **Coal**.

**Final Answer**: Coal requires the highest amount of excess air for combustion.

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