Study the following statements and select the correct ones .
(i) Methanogens are archaebacteria which fixes atmsopheric nitrogen
(ii) Nostic is a filamentous blue green alga which fixes atmospheric nitrogen.
(iii) Mycoplasma lack cell wall and can surive without oxygen.

Options

A. (i) and (ii)
B. (i) and (iii)
C. (ii) and (iii)
D. (i) , (ii) and (iii)

Answer

To solve the question, we will analyze each statement one by one to determine their correctness.

### Step-by-Step Solution:

1. **Analyze Statement (i)**:
- **Statement**: Methanogens are archaebacteria which fix atmospheric nitrogen.
- **Analysis**: Methanogens are indeed archaebacteria, but they do not fix atmospheric nitrogen. Instead, they are known for producing methane gas. Therefore, this statement is **incorrect**.

2. **Analyze Statement (ii)**:
- **Statement**: Nostoc is a filamentous blue-green alga which fixes atmospheric nitrogen.
- **Analysis**: Nostoc is classified as a cyanobacterium (often referred to as blue-green algae) and is known for its ability to fix atmospheric nitrogen, converting it into ammonia. Thus, this statement is **correct**.

3. **Analyze Statement (iii)**:
- **Statement**: Mycoplasma lack cell wall and can survive without oxygen.
- **Analysis**: Mycoplasma are unique in that they lack a cell wall, which allows them to take on various shapes (hence the term "joker" of microorganisms). They can also survive in anaerobic conditions (without oxygen). Therefore, this statement is **correct**.

### Conclusion:
- The correct statements are:
- Statement (ii): Nostoc is a filamentous blue-green alga which fixes atmospheric nitrogen.
- Statement (iii): Mycoplasma lack cell wall and can survive without oxygen.

Thus, the correct answer is that statements (ii) and (iii) are correct.

### Final Answer:
- The correct statements are (ii) and (iii).

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