What is nitrogen cycle? List the five main process that it is composed of.

Explanation

### Step-by-Step Solution:

1. **Definition of Nitrogen Cycle**:
The nitrogen cycle is a series of processes through which atmospheric nitrogen is converted into a form that can be utilized by living organisms, particularly plants. This cycle also involves the return of nitrogen back to the atmosphere.

2. **Five Main Processes of the Nitrogen Cycle**:
- **Nitrogen Fixation**: This is the process by which atmospheric nitrogen (N₂) is converted into ammonia (NH₃) or related compounds in the soil. This conversion is primarily carried out by certain bacteria and some plants.

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