Select the incorrect statement about the methanogens.

Options

A. These belong to archaebacteria
B. These live in marshy areas.
C. It produces biogas which is purely methane
D. These are found in the gut of ruminants

Answer

To solve the question regarding the incorrect statement about methanogens, we will analyze each option provided in the question step by step.

### Step 1: Understand what Methanogens are
Methanogens are a group of microorganisms that produce methane as a metabolic byproduct in anoxic conditions. They are primarily found in anaerobic environments.

### Step 2: Analyze each option

1. **Option 1: Methanogens belong to archaebacteria.**
- **Analysis:** This statement is correct. Methanogens are indeed classified under the domain Archaea, specifically within the group of archaebacteria.

2. **Option 2: Methanogens live in marshy areas.**
- **Analysis:** This statement is partially correct. While methanogens are found in marshy areas, they are not limited to these environments. They can also be found in other anaerobic environments such as the guts of ruminants and sediments of lakes. Therefore, this statement is misleading.

3. **Option 3: Methanogens produce biogas which is purely methane.**
- **Analysis:** This statement is incorrect. Biogas produced by methanogens is not purely methane; it typically contains 55-65% methane along with other gases such as carbon dioxide, hydrogen sulfide, and traces of other gases. Thus, this statement is indeed incorrect.

4. **Option 4: Methanogens are found in the gut of ruminants.**
- **Analysis:** This statement is correct. Methanogens are commonly found in the digestive tracts of ruminants, where they play a crucial role in the digestion of cellulose.

### Conclusion
Based on the analysis, the incorrect statement about methanogens is **Option 3**, which claims that biogas produced by methanogens is purely methane.

### Final Answer
**The incorrect statement about methanogens is: Option 3 - It produces biogas which is purely methane.**

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