The nitrogen molecules present in air can be converted into nitrates and nitrites by

Options

A. a biological process of nitrogen fixing bacteria present in soil
B. a biological process of carbon fixing factor present in soil
C. any of the industries manufacturing nitrogeneous compounds
D. the plants used as cereal crops in field

Explanation

**Step-by-Step Solution:**

1. **Understanding Nitrogen in the Atmosphere**: Nitrogen makes up about 78% of the Earth's atmosphere. It is essential for life, particularly in the formation of proteins and nucleic acids (DNA and RNA).

2. **Need for Conversion**: The nitrogen gas (N₂) present in the atmosphere cannot be directly used by plants or animals. It must be converted into a usable form, specifically nitrates (NO₃⁻) and nitrites (NO₂⁻).

3. **Nitrogen Fixation**: The process of converting nitrogen gas into nitrates and nitrites is called nitrogen fixation. This process is crucial for making nitrogen available to living organisms.

4. **Role of Bacteria**: Nitrogen fixation is primarily carried out by certain bacteria that are present in the soil. These bacteria can convert atmospheric nitrogen into nitrates and nitrites.

5. **Example of Nitrogen-Fixing Bacteria**: One well-known example of nitrogen-fixing bacteria is Azotobacter. These bacteria play a significant role in the nitrogen cycle by facilitating the conversion of nitrogen gas into forms that can be utilized by plants.

6. **Identifying the Correct Answer**: Based on the information provided, the correct answer to the question is that nitrogen molecules in the air are converted into nitrates and nitrites by a biological process involving nitrogen-fixing bacteria present in the soil.

**Final Answer**: The nitrogen molecules present in air can be converted into nitrates and nitrites by a biological process of nitrogen-fixing bacteria present in the soil.

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