The brown compound formed in the ring test for nitrates contains the ion

Options

A. `[Fe(H_(2)O)_(5)NO]^(3+)`
B. `[Fe(H_(2)O)_(5)NO]^(2+)`
C. `[Fe(H_(2)O)_(5)NO]^(4+)`
D. `[Fe(H_(2)O)_(5)NO]`

Answer

To solve the question regarding the brown compound formed in the ring test for nitrates, we can follow these steps:

### Step-by-Step Solution:

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

2. **Reagents Involved**: The main reagents used in this test are ferrous sulfate (FeSO4), concentrated sulfuric acid (H2SO4), and nitric acid (HNO3).

3. **Initial Reaction**: When ferrous sulfate reacts with concentrated sulfuric acid and nitric acid, it forms a complex. The reaction can be represented as:
\[ 3 \text{FeSO}_4 + 6 \text{H}_2\text{SO}_4 + 2 \text{HNO}_3 \rightarrow 3 \text{Fe}_2(\text{SO}_4)_3 + 6 \text{H}_2\text{O} + 2 \text{NO} \]

4. **Formation of the Brown Complex**: The nitric oxide (NO) produced in the reaction then reacts with ferrous sulfate to form a brown ring complex. The reaction can be represented as:
\[ \text{FeSO}_4 + \text{NO} + 5 \text{H}_2\text{O} \rightarrow \text{[Fe(H}_2\text{O)}_5\text{NO]}^{2+} + \text{SO}_4^{2-} \]

5. **Identifying the Ion in the Brown Compound**: The brown ring complex formed is [Fe(H2O)5NO]^{2+}. This indicates that the ion present in the brown compound is the nitrosyl ion (NO) combined with the ferrous ion (Fe^{2+}).

6. **Conclusion**: Therefore, the brown compound formed in the ring test for nitrates contains the ion NO (nitrosyl ion).

### Final Answer:
The brown compound formed in the ring test for nitrates contains the ion **NO** (nitrosyl ion).

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