Which gas cannot be used as a fuel ?

Options

A. C.N.G.
B. L.P.G.
C. Oxygen
D. Hydrogen

Answer

To determine which gas cannot be used as a fuel, let's analyze the options provided:

1. **CNG (Compressed Natural Gas)**: CNG is a fuel that is used in vehicles and for heating. It is a clean-burning fossil fuel, making it a viable option for energy.

2. **LPG (Liquefied Petroleum Gas)**: LPG is another common fuel used for heating, cooking, and in some vehicles. It is derived from crude oil and natural gas and is widely used as a fuel source.

3. **Oxygen**: Oxygen is essential for combustion, as it supports the burning of fuels. However, oxygen itself is not a fuel; it is an oxidizer. It is primarily used for breathing and in various industrial processes but cannot be burned to produce energy.

4. **Hydrogen**: Hydrogen can be used as a fuel, particularly in fuel cells and combustion engines. It is a clean fuel that produces only water when burned.

Based on this analysis, the gas that cannot be used as a fuel is **Oxygen**.

### Step-by-Step Solution:
1. **Identify the gases listed**: CNG, LPG, Oxygen, and Hydrogen.
2. **Evaluate each gas**:
- CNG: Used as a fuel.
- LPG: Used as a fuel.
- Oxygen: Not used as a fuel; it supports combustion.
- Hydrogen: Used as a fuel.
3. **Conclude which gas cannot be used as a fuel**: Oxygen is the gas that cannot be used as a fuel.

### Final Answer:
The gas that cannot be used as a fuel is **Oxygen**.