The important gas which was absent during the origin of life on Earth:

Options

A. oxygen gas
B. hydrogen gas
C. nitrogen gas
D. carbon dioxide gas

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks for an important gas that was absent during the origin of life on Earth. We need to identify which gas among the options provided was not present in the primitive atmosphere.

2. **Identifying the Options**: The options given are:
- A) Oxygen gas
- B) Hydrogen gas
- C) Nitrogen gas
- D) Carbon dioxide gas

3. **Analyzing the Primitive Atmosphere**: According to scientific theories, particularly the Oparin theory, the primitive atmosphere of Earth was reducing in nature. This means that it contained various gases that contributed to a reducing environment.

4. **Listing Gases Present in the Primitive Atmosphere**: The gases that were present in the primitive atmosphere included:
- Hydrogen gas
- Nitrogen gas
- Methane
- Ammonia
- Water vapor
- Carbon dioxide

5. **Identifying the Absent Gas**: Among the gases listed, oxygen gas was notably absent. This is significant because oxygen is essential for aerobic respiration, which is a process used by many organisms to generate energy.

6. **Conclusion**: Based on the analysis, the important gas that was absent during the origin of life on Earth is **oxygen gas**.

7. **Final Answer**: Therefore, the correct answer is **A) Oxygen gas**.

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