Nitrogen cycle involves many compounds. Which illustration correctly depicts the nitrogen cycle?

Options

A.
B.
C.
D.

Answer

### Step-by-Step Solution:

1. **Understanding the Nitrogen Cycle**: The nitrogen cycle is a natural process that involves the conversion of nitrogen from the atmosphere into various forms that can be used by living organisms. It includes several key processes: nitrogen fixation, ammonification, nitrification, and denitrification.

2. **Nitrogen Fixation**: The cycle begins with nitrogen fixation, where certain bacteria in the soil convert atmospheric nitrogen (N₂) into ammonia (NH₃). This process is crucial because plants cannot directly use atmospheric nitrogen.

3. **Ammonification**: Once nitrogen is fixed into ammonia, it can be further processed through ammonification, where organic matter is decomposed by bacteria, releasing ammonia into the soil.

4. **Nitrification**: The next step is nitrification, which occurs in two stages:
- First, nitrococcus bacteria convert ammonia into nitrite (NO₂⁻).
- Then, nitrobacter bacteria convert nitrite into nitrate (NO₃⁻), which is a form that plants can readily absorb.

5. **Denitrification**: Finally, the cycle is completed through denitrification, where bacteria such as Theobacillus or Pseudomonas convert nitrates back into nitrogen gas (N₂), releasing it back into the atmosphere.

6. **Identifying the Correct Illustration**: To determine which illustration correctly depicts the nitrogen cycle, look for one that includes:
- Nitrogen fixation (conversion of N₂ to NH₃)
- Ammonification (release of NH₃ from organic matter)
- Nitrification (conversion of NH₃ to NO₂⁻ and then to NO₃⁻)
- Denitrification (conversion of NO₃⁻ back to N₂)

7. **Conclusion**: Based on the processes described, the correct illustration of the nitrogen cycle will be the one that accurately represents all these stages. According to the video, the correct answer is option number 1, as it includes all the necessary components of the nitrogen cycle.