Which one of the folloiwng is wrongly statement?

Options

A. Phosphorous is a constitutent of cell membrane, certain nucleic acids and all proteins
B. Nitrosomonas and Nitrobacter are chemoautotrophs
C. Anabaena and Nostoc are capable of fixing nitrogen in free-living state also
D. Root nodule forming nitrogen fixers live as aerobes under free living conditions.

Answer

To determine which statement is incorrect among the given options, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Analyze Statement 1**:
- The statement claims that phosphorus is a constituent of cell membranes, nucleic acids, and all proteins.
- **Cell Membrane**: Phospholipids, which make up the cell membrane, contain phosphate groups, confirming that phosphorus is indeed a part of the cell membrane.
- **Nucleic Acids**: Both DNA and RNA have a phosphate backbone, indicating that phosphorus is a component of nucleic acids.
- **Proteins**: However, proteins do not universally contain phosphorus. They are primarily made up of carbon, hydrogen, nitrogen, and oxygen. Hence, this statement is incorrect because phosphorus is not a constituent of all proteins.

2. **Analyze Statement 2**:
- This statement mentions nitrosomonas and nitrobacter as chemo-autotrophs involved in nitrification.
- Chemo-autotrophs are organisms that obtain energy from chemical compounds and use carbon dioxide as their carbon source. This statement is accurate.

3. **Analyze Statement 3**:
- The statement indicates that NMN (Nostoc) can fix nitrogen in a free-living state.
- Nostoc is indeed known for its ability to fix atmospheric nitrogen into ammonia, and it can do so in a free-living state. This statement is correct.

4. **Analyze Statement 4**:
- This statement asserts that root nodule-forming nitrogen fixers can live as aerobic organisms under free-living conditions.
- Root nodule-forming nitrogen fixers, such as Rhizobium, do require oxygen for growth in free-living conditions, making this statement correct as well.

### Conclusion:
After analyzing all the statements, we find that the first statement is the only incorrect one. Therefore, the answer is **Option 1**.