Which of the following statements about the chemical process of `N_(2)` fixation in cells is true

Options

A. it is enhanced by high `O_(2)` concentrations
B. Very little energy in the form of ATP is needed
C. All three bonds between nitrogen atoms are broken simultaneously
D. Hydrogen atoms are added to nitrogen to form `NH_(3)` molecules

Answer

To determine which statement about the chemical process of nitrogen fixation in cells is true, we will analyze each given option step by step.

### Step-by-Step Solution:

1. **Understanding Nitrogen Fixation**:
- Nitrogen fixation is the process by which atmospheric nitrogen (N₂) is converted into ammonia (NH₃) or related compounds in soil and water, making it available for uptake by plants.

2. **Evaluating Option 1**:
- **Statement**: "It is enhanced by high oxygen concentration."
- **Analysis**: Nitrogen fixation is actually inhibited by high oxygen concentrations. Oxygen can interfere with the nitrogenase enzyme that catalyzes the fixation process.
- **Conclusion**: This statement is **incorrect**.

3. **Evaluating Option 2**:
- **Statement**: "It is not enhanced by the concentration of oxygen during the chemical nitrogen fixation."
- **Analysis**: This statement is somewhat misleading. While it is true that nitrogen fixation is not enhanced by oxygen, it is more accurate to say that nitrogen fixation is inhibited by oxygen. Hence, this statement could be considered **incorrect** in the context of the question asking for a true statement.

4. **Evaluating Option 3**:
- **Statement**: "All three bonds between nitrogen atoms are broken simultaneously."
- **Analysis**: In nitrogen fixation, the triple bond between nitrogen atoms is broken, but this does not happen simultaneously for all three bonds. The process involves a series of steps where bonds are broken and hydrogen is added.
- **Conclusion**: This statement is **incorrect**.

5. **Evaluating Option 4**:
- **Statement**: "Hydrogen atoms are added to nitrogen to form NH₃ molecule."
- **Analysis**: During nitrogen fixation, nitrogen (N₂) is indeed converted to ammonia (NH₃) by the addition of hydrogen atoms. Specifically, three hydrogen atoms are added to one nitrogen atom to form ammonia, requiring a total of six hydrogen atoms for two nitrogen atoms to form two ammonia molecules.
- **Conclusion**: This statement is **correct**.

### Final Answer:
The true statement about the chemical process of nitrogen fixation in cells is: **"Hydrogen atoms are added to nitrogen to form NH₃ molecule."**