Primary atmosphere was

Options

A. Reducing
B. Oxidising
C. Rich in ozone
D. Rich in `NO_2`

Answer

### Step-by-Step Solution

1. **Understanding Primary Atmosphere**: The primary atmosphere refers to the original atmosphere of the Earth during its early formation. This was a time when the Earth was still undergoing significant geological and chemical changes.

2. **Nature of the Primary Atmosphere**: The primary atmosphere was characterized as a reducing atmosphere. This means that it lacked free oxygen (O2), which is crucial for an oxidizing atmosphere.

3. **Absence of Photosynthetic Organisms**: During the time of the primary atmosphere, there were no organisms capable of photosynthesis, such as plants or photosynthetic bacteria. This absence is significant because photosynthesis is the process that produces oxygen.

4. **Consequences of a Reducing Atmosphere**: The lack of oxygen created a reducing environment, which is conducive to the formation of organic compounds. This environment allowed simple molecules to combine and form more complex organic molecules, which is essential for the origin of life.

5. **Elimination of Incorrect Options**:
- An oxidizing atmosphere would imply the presence of oxygen, which was not the case.
- A rich ozone (O3) environment would also require the presence of oxygen, which was absent in the primary atmosphere.
- A rich environment in nitrogen dioxide (NO2) is not accurate for the primary atmosphere.

6. **Conclusion**: Therefore, the primary atmosphere of the Earth was a reducing atmosphere, which played a crucial role in the development of life.

### Final Answer
The primary atmosphere was a reducing atmosphere.

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