Methanogen do rot produce:

Options

A. Oxygen
B. Methane
C. Hydrogen sulphide
D. Carbon dioxide

Explanation

### Step-by-Step Solution:

1. **Understanding Methanogens**:
- Methanogens are a type of archaea that thrive in anaerobic (oxygen-free) environments. They are known for their ability to produce methane as a metabolic byproduct.

2. **Identifying the Products of Methanogens**:
- The primary product of methanogens is methane (CH₄). They also produce other gases such as carbon dioxide (CO₂) and hydrogen sulfide (H₂S) during their metabolic processes.

3. **Analyzing the Options**:
- The question provides four options regarding what methanogens do not produce:
- Option A: Oxygen (O₂)
- Option B: Methane (CH₄)
- Option C: Hydrogen Sulfide (H₂S)
- Option D: Carbon Dioxide (CO₂)

4. **Eliminating Incorrect Options**:
- **Option B (Methane)**: This is incorrect because methanogens are known for producing methane.
- **Option C (Hydrogen Sulfide)**: This is also incorrect as methanogens can produce hydrogen sulfide.
- **Option D (Carbon Dioxide)**: This is incorrect since carbon dioxide is also a byproduct of methanogenic activity.

5. **Identifying the Correct Answer**:
- The only option left is **Option A (Oxygen)**. Methanogens do not produce oxygen as they thrive in anaerobic conditions.

6. **Conclusion**:
- Therefore, the correct answer to the question "Methanogen do not produce:" is **Option A: Oxygen**.