What happened to `NH_3` present in primary atmosphere during its conversion to secondary atmosphere?

Options

A. Its concentration decreased due to excessive formation of oxygen
B. Most of it got oxidised to nitrogen oxides
C. Got oxidised to `N_2` and water
D. Was absorbed by photoautotrophs

Answer

**Step-by-Step Solution:**

1. **Understanding the Primary Atmosphere**: The primary atmosphere of Earth was composed of various gases, including ammonia (NH₃). This atmosphere existed in the early stages of Earth's formation.

2. **Transition to Secondary Atmosphere**: As Earth evolved, the primary atmosphere began to change. This transition is referred to as the conversion to the secondary atmosphere.

3. **Role of Ammonia (NH₃)**: During this conversion, ammonia, which was abundant in the primary atmosphere, underwent chemical changes.

4. **Oxidation Process**: The ammonia present in the primary atmosphere was primarily converted into nitrogen oxides (NOx). This process is known as oxidation, where ammonia reacts with other substances (like oxygen) to form nitrogen oxides such as NO, NO₂, and NO₃.

5. **Resulting Composition**: As a result of this oxidation, the concentration of ammonia in the atmosphere significantly decreased, leading to very little or no ammonia being present in the secondary atmosphere.

6. **Conclusion**: Therefore, the main outcome of the conversion of ammonia in the primary atmosphere was that it was largely oxidized into nitrogen oxides.

**Final Answer**: Most of the ammonia (NH₃) present in the primary atmosphere was converted into nitrogen oxides (NOx) during its transition to the secondary atmosphere.

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