Which of the following is incorrect about methanogens ?

Options

A. They are archaebacteria .
B. They live in marshy area.
C. Methane is their preferred carbon source .
D. They persist in guts of several ruminate animals and they produces biogas from their dung.

Answer

To solve the question "Which of the following is incorrect about methanogens?", we will analyze each of the provided options regarding methanogens and determine which statement is incorrect.

### Step-by-Step Solution:

1. **Understanding Methanogens**:
- Methanogens are a group of microorganisms that produce methane as a metabolic by-product in anoxic (absence of oxygen) conditions. They are primarily found in environments such as marshes, wetlands, and the digestive tracts of ruminant animals.

2. **Analyzing the Options**:
- **Option A**: "They are archaebacteria."
- This statement is **correct**. Methanogens belong to the domain Archaea, specifically classified as archaebacteria.

- **Option B**: "They live in marshy areas."
- This statement is also **correct**. Methanogens thrive in marshy and anaerobic environments where they can produce methane.

- **Option C**: "Methane is their preferred carbon source."
- This statement is **incorrect**. Methanogens do not prefer methane as a carbon source; instead, they utilize carbon dioxide (CO2) and hydrogen (H2) to produce methane.

- **Option D**: "They persist in the gut of severe ruminant animals and they produce biogas from their dung."
- This statement is **correct**. Methanogens are indeed found in the digestive systems of ruminants (like cows) and contribute to the production of biogas from their waste.

3. **Identifying the Incorrect Statement**:
- After analyzing all options, we find that **Option C** is the incorrect statement regarding methanogens.

### Conclusion:
The correct answer is **Option C**: "Methane is their preferred carbon source."