In brown ring test for nitrate ions, brown ring is formed due to complex

Options

A. `[Fe(H_(2)O)_(6)}^(2+)`
B. `[Fe(H_(2)O)_(5)NO]^(2+)`
C. `[Fe(H_(2)O)_(5)NO]^(3+)`
D. `[Fe(H_(2)O)_(5)NO_(2)]^(2+)`

Answer

To solve the question regarding the brown ring test for nitrate ions, we will follow these steps:

### Step 1: Understand 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.

**Hint:** Familiarize yourself with the purpose of the brown ring test and the ions involved.

### Step 2: Identify the Reactants
In the test, a sample containing nitrate ions is mixed with iron(II) sulfate (FeSO4) solution. Concentrated sulfuric acid (H2SO4) is then added.

**Hint:** Know the chemical species involved in the reaction: nitrate ions, iron(II) ions, and protons from sulfuric acid.

### Step 3: Write the Reaction
The nitrate ion reacts with iron(II) ions and protons to produce nitric oxide (NO), iron(III) ions (Fe3+), and water (H2O). The balanced equation for this reaction is:

\[ \text{NO}_3^- + \text{Fe}^{2+} + \text{H}^+ \rightarrow \text{NO} + \text{Fe}^{3+} + \text{H}_2\text{O} \]

**Hint:** Ensure that you can balance chemical equations and understand the stoichiometry involved.

### Step 4: Formation of the Brown Ring Complex
The iron(III) ions (Fe3+) produced in the reaction can form a complex with water and nitric oxide. The complex formed is:

\[ \text{Fe(H}_2\text{O})_5\text{NO}^{2+} \]

This complex is responsible for the characteristic brown ring observed at the interface of the two layers in the test.

**Hint:** Recognize that the formation of a complex is key to the visual indication of the test.

### Step 5: Identify the Correct Option
From the information provided, the brown ring complex is represented as:

\[ \text{Fe(H}_2\text{O})_5\text{NO}^{2+} \]

Thus, the correct answer to the question is the option that states this complex.

**Hint:** Cross-check the options given in the question to find the one that matches the complex formula.

### Final Answer
The brown ring is formed due to the complex \(\text{Fe(H}_2\text{O})_5\text{NO}^{2+}\).

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