Which of the following is not used as fuel?

Options

A. LPG
B. CNG
C. hydrogen
D. oxygen

Answer

To determine which of the following is not used as fuel, we need to understand what fuel is. Fuel is a substance that reacts with oxygen to produce energy.

### Step-by-Step Solution:

1. **Define Fuel**: Fuel is a substance that can react with oxygen to release energy. This energy is often in the form of heat and light.

2. **Identify Common Fuels**: Common examples of fuels include:
- **LPG (Liquefied Petroleum Gas)**: A mixture of propane and butane, used widely for cooking and heating.
- **CNG (Compressed Natural Gas)**: Mainly composed of methane, used as an alternative to gasoline and diesel.
- **Hydrogen**: When burned, it reacts with oxygen to produce water and energy.

3. **Analyze the Options**: The question provides several options, and we need to identify which one is not a fuel.
- **LPG**: This is a fuel.
- **CNG**: This is also a fuel.
- **Hydrogen**: This is a fuel as well.
- **Oxygen**: This is not a fuel because it does not react with itself to produce energy.

4. **Conclusion**: Since oxygen does not react with itself to produce energy, it does not qualify as a fuel.

### Final Answer:
**Oxygen** is not used as fuel.

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