Reaction carried out by `N_(2)` fixing microbes include
`2NH_(3)+3O_(2)to2NO_(2)^(-)+2H^(+)+2H_(2)O` …(i)
`2NO_(2)^(-)+O_(2)to2NO_(3)^(-)` ….(ii) Which of the following statements about these equations is not true?

Options

A. Step(i) is carried out by Nitrosomonas or Nitrosomonas
B. Step (ii) is carried out by Nitrobacter
C. Both steps (i) and (ii) can be called ni- trification
D. Bacteria carrying out these steps are usually photoautotrophs

Answer

To solve the question regarding the reactions carried out by nitrogen-fixing microbes, we need to analyze the provided equations and the statements about them. Here’s a step-by-step breakdown of the solution:

### Step 1: Understand the Reactions
The two reactions given are:
1. \( 2NH_3 + 3O_2 \rightarrow 2NO_2^- + 2H^+ + 2H_2O \) (Reaction i)
2. \( 2NO_2^- + O_2 \rightarrow 2NO_3^- \) (Reaction ii)

These reactions are part of the nitrification process, where ammonia is first converted to nitrite and then to nitrate.

### Step 2: Identify the Bacteria Involved
- The first reaction (i) is typically carried out by **Nitrosomonas**, which converts ammonia (NH3) to nitrite (NO2^-).
- The second reaction (ii) is carried out by **Nitrobacter**, which converts nitrite (NO2^-) to nitrate (NO3^-).

### Step 3: Define Nitrification
Both reactions are part of the nitrification process. Nitrification is the biological oxidation of ammonia to nitrite followed by the oxidation of nitrite to nitrate.

### Step 4: Classify the Bacteria
The bacteria involved in these reactions are classified as:
- **Chemoautotrophs**: They derive energy from the oxidation of inorganic molecules (like ammonia) and use carbon dioxide as their carbon source.

### Step 5: Evaluate the Statements
Now, we need to evaluate the statements regarding these reactions. The question asks for the statement that is **not true**.

- **True Statements**:
- The reactions are indeed part of the nitrification process.
- Nitrosomonas and Nitrobacter are the correct bacteria for the respective reactions.

- **False Statement**:
- If any statement claims that these bacteria are **photoautotrophs**, it would be incorrect, as they are **chemoautotrophs**.

### Conclusion
The statement that is not true regarding the reactions is the one that incorrectly classifies the bacteria as photoautotrophs instead of chemoautotrophs.

### Final Answer
The statement about these equations that is not true is that the bacteria involved in these reactions are photoautotrophs.

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