Nitrates is confirmed by ring test.The brown colour of the ring is due to formation of:

Options

A. ferrous nitrite
B. nitroso ferrous sulphate
C. ferrous nitrate
D. `FeSO_(4).NO_(2)`

Explanation

To determine the brown color of the ring formed in the ring test for nitrates, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Ring Test**: The ring test is a qualitative analysis method used to confirm the presence of nitrate ions (NO3-) in a solution.

2. **Reagents Involved**: The key reagents involved in the ring test are:
- Nitrate ions (NO3-)
- Concentrated sulfuric acid (H2SO4)
- Iron (Fe) in the form of filings or powder

3. **Reaction Process**: When these reagents are mixed, a series of reactions occur:
- The nitrate ion reacts with concentrated sulfuric acid and iron, leading to the formation of various products including nitrogen oxides and iron complexes.

4. **Formation of the Brown Ring**: The specific reaction that leads to the formation of the brown ring can be summarized as follows:
- Nitrate ion (NO3-) reacts with iron (Fe) and sulfuric acid (H2SO4) to produce:
- Nitrogen monoxide (NO)
- Iron(III) ions (Fe3+)
- Sulfate ions (SO4^2-)
- The iron(II) ions (Fe2+) then react with the nitrogen monoxide (NO) and sulfate ions to form a complex known as nitroso ferrous sulfate.

5. **Identifying the Brown Complex**: The brown color of the ring is specifically due to the formation of the complex:
- **Nitroso ferrous sulfate (FeSO4.NO)**

6. **Conclusion**: Thus, the brown color of the ring observed in the ring test for nitrates is due to the formation of nitroso ferrous sulfate.

### Final Answer:
The brown color of the ring is due to the formation of **nitroso ferrous sulfate (FeSO4.NO)**.

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