Liqiuid propellant is a

Options

A. `H_(2)O`
B. petrol
C. hydrazine
D. All of these

Explanation

### Step-by-Step Solution:

1. **Understanding Liquid Propellant**:
- A liquid propellant is a substance that is used to propel rockets, jets, or airplanes. It is a fuel that, upon combustion, produces a force that pushes the vehicle forward.

2. **Analyzing the Options**:
- **Option 1: H2O (Water)**: Water does not combust; therefore, it cannot be used as a liquid propellant.
- **Option 2: Petrol**: While petrol does combust, it is not suitable as a liquid propellant for rockets and jets because it does not release enough energy to propel these vehicles effectively.
- **Option 3: Hydrogen**: Hydrogen can be used as a fuel, but it is typically in gaseous form and not considered a liquid propellant in this context.
- **Option 4: All of these**: Since H2O and petrol are not suitable, this option is also incorrect.

3. **Identifying the Correct Liquid Propellant**:
- The most suitable liquid propellant among the options provided is **Hydrazine**.
- Hydrazine is a colorless liquid with a low melting point (2.0 °C) and a boiling point of 113.5 °C. It reacts readily with moisture, producing a high-energy reaction that can be harnessed for propulsion in rockets and jets.

4. **Conclusion**:
- The correct answer is **Hydrazine**, as it is specifically used as a liquid propellant due to its properties and energy release upon reaction.

### Final Answer:
The correct liquid propellant is **Hydrazine** (Option 3).

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