Nitrate formation by the following reaction is accomplished by
`2NO_2^(-)+O_2rarr2NO_(3)^-`

Options

A. Nitrococcus
B. Nitrosomonas
C. Nitrobacter
D. Thiobacillus or Pseudomonas

Answer

To solve the question regarding the nitrate formation reaction `2NO2^(-) + O2 → 2NO3^(-)`, we need to identify which organism is responsible for this conversion. Here’s a step-by-step breakdown of the solution:

### Step 1: Understand the Reaction
The reaction given involves the conversion of nitrite (NO2^-) to nitrate (NO3^-). This process is part of the larger nitrogen cycle and is known as nitrification.

**Hint:** Identify the reactants and products in the reaction to understand what is being transformed.

### Step 2: Define Nitrification
Nitrification is a two-step biological process where ammonia is first oxidized to nitrite and then nitrite is oxidized to nitrate. The first step is carried out by ammonia-oxidizing bacteria, while the second step is performed by nitrite-oxidizing bacteria.

**Hint:** Remember that nitrification involves two distinct groups of bacteria for each step of the process.

### Step 3: Identify the Organisms
The organisms involved in the nitrification process include:
- **Ammonia-oxidizing bacteria** (e.g., Nitrosomonas) convert ammonia to nitrite.
- **Nitrite-oxidizing bacteria** (e.g., Nitrobacter) convert nitrite to nitrate.

**Hint:** Focus on which group of bacteria is responsible for the specific conversion of nitrite to nitrate.

### Step 4: Analyze the Options
The options provided are:
1. Nitrococcus
2. Nitrosomonas
3. Nitrobacter
4. Thiobacillus
5. Pseudomonas

- **Nitrococcus** and **Nitrosomonas** are involved in the first step (ammonia to nitrite).
- **Nitrobacter** is the organism that specifically oxidizes nitrite to nitrate, which is what we need.
- **Thiobacillus** and **Pseudomonas** do not play a role in the nitrification process.

**Hint:** Eliminate options that do not relate to the conversion of nitrite to nitrate.

### Step 5: Conclusion
Based on the analysis, the correct answer is **Nitrobacter**, as it is the organism responsible for the conversion of nitrite (NO2^-) to nitrate (NO3^-).

**Final Answer:** Nitrate formation by the following reaction is accomplished by **Nitrobacter**.