Assertion (A): Methanogens do not produce oxygen. Reason (R) : Methanogens are obligate anaerobic micro-organisms.

Options

A. Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
B. Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
C. Assertion (A) is true but reason (R) is false.
D. Assertion (A) is false but reason (R) is true.

Explanation

### Step-by-Step Solution:

1. **Understanding the Assertion (A)**: The assertion states that "Methanogens do not produce oxygen." This is a factual statement about methanogens, which are a group of microorganisms.

2. **Understanding the Reason (R)**: The reason provided is that "Methanogens are obligate anaerobic microorganisms." This means that methanogens thrive in environments devoid of oxygen.

3. **Analyzing the Relationship**: Since methanogens are obligate anaerobes, they do not engage in processes that would produce oxygen. Instead, they carry out anaerobic respiration, which does not involve oxygen.

4. **Conclusion**: Both the assertion and the reason are true. The reason correctly explains why methanogens do not produce oxygen, as their anaerobic nature prevents them from doing so.

5. **Final Answer**: Therefore, the correct option is that both the assertion and the reason are true, and the reason is the correct explanation of the assertion.