Select the incorrect statement w.r.t methanogens.

Options

A. They are Gram negative
B. Obligate anaerobes
C. Chemoheterotrophs
D. Produce methane gas from `CO_(2)`

Answer

To determine the incorrect statement with respect to methanogens, we need to analyze the given statements one by one:

1. **They are gram-negative.**
- Methanogens are indeed classified as gram-negative bacteria. This statement is correct.

2. **They are obligate anaerobes.**
- Methanogens require an oxygen-free environment to survive, which makes them obligate anaerobes. This statement is also correct.

3. **They are chemoheterotrophs.**
- Chemoheterotrophs are organisms that obtain their energy and carbon from organic compounds. Methanogens primarily produce methane from carbon dioxide and hydrogen, and they do not fit the definition of chemoheterotrophs. This statement is incorrect.

4. **They produce methane gas from carbon dioxide.**
- Methanogens are known for their ability to produce methane from carbon dioxide and hydrogen. This statement is correct.

Based on the analysis, the incorrect statement regarding methanogens is the third one: "They are chemoheterotrophs."