A peculiar odour found in marshy areas and cow sheds is of gas produced by

Options

A. Archaebacteria
B. Cyanobacteria
C. Slime moulds
D. Mycoplasma.

Answer

### Step-by-Step Solution:

1. **Identify the Source of the Odour**: The question mentions a peculiar odour found in marshy areas and cow sheds. This odour is typically associated with the presence of methane gas.

2. **Understand the Role of Microbes**: The peculiar odour in these areas is due to the production of methane gas by certain types of microorganisms.

3. **Recognize the Type of Microorganism**: The microorganisms responsible for the production of methane are known as methanogens. These are a specific group of archaebacteria.

4. **Classify Methanogens**: Methanogens are classified under the domain Archaea, specifically within the group of archaebacteria. They thrive in anaerobic conditions, which are prevalent in marshy areas and in the decomposition of organic matter in cow dung.

5. **Evaluate the Options**: The options given in the question are:
- A) Archaebacteria
- B) Cyanobacteria
- C) Slime molds
- D) Mycoplasma

- **Option A (Archaebacteria)**: Correct, as methanogens are a type of archaebacteria.
- **Option B (Cyanobacteria)**: Incorrect, as they are photosynthetic and do not produce methane.
- **Option C (Slime molds)**: Incorrect, as they are eukaryotic and do not produce methane.
- **Option D (Mycoplasma)**: Incorrect, as they are bacteria without cell walls and do not produce methane.

6. **Conclusion**: The correct answer to the question is **A) Archaebacteria**, as they include methanogens which produce methane gas responsible for the peculiar odour.