Use of helium is preferred over use of hydrogen in airships (e.g., blimps ) because

Options

A. helium is chemically less reactive
B. helium has a lower density
C. both of the above
D. none of the above.

Explanation

To solve the question of why helium is preferred over hydrogen in airships (e.g., blimps), we can analyze the properties of both gases step by step.

### Step-by-Step Solution:

1. **Identify the Properties of Helium and Hydrogen**:
- Helium (He) is a noble gas, which means it has a complete outer electron shell. This gives it a stable electronic configuration.
- Hydrogen (H), on the other hand, is not a noble gas and has only one electron in its outer shell, making it reactive.

2. **Chemical Reactivity**:
- Due to its noble gas nature, helium is chemically unreactive. It does not readily form compounds or react with other elements.
- Hydrogen is chemically reactive and can easily react with other substances, including oxygen, which can lead to combustion.

3. **Safety Considerations**:
- The reactivity of hydrogen poses a significant safety risk. In the presence of oxygen, hydrogen can ignite and cause explosions, especially in an airship where flammable materials are present.
- Helium, being non-flammable and chemically inert, presents no such risks, making it a safer option for use in airships.

4. **Cost Considerations**:
- While helium is more expensive than hydrogen, the safety benefits of using helium outweigh the cost factor. The risk of using hydrogen in airships is much higher due to its flammability.

5. **Density Comparison**:
- Helium is less dense than air, which allows airships to float. Hydrogen is even less dense than helium, but the safety concerns regarding hydrogen's reactivity make helium the preferred choice despite its higher density compared to hydrogen.

6. **Conclusion**:
- The primary reason for preferring helium over hydrogen in airships is its chemical inertness and safety. Thus, the correct answer to the question is that helium is preferred because it is chemically less reactive.

### Final Answer:
Helium is preferred over hydrogen in airships because helium is chemically less reactive.

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