In test of `NO_(3)^(-)` ion, the dark brown ring complex is formed, which is true of this complex?

Options

A. the colour is due to charge transfer spectra
B. iron and NO both have +1 charge
C. The complex species can be represented as `[Fe^(I)(H_(2)O)_(5)NO]^(2+)`
D. Iron has +2 oxidation state and NO is neutral

Explanation

To solve the question regarding the dark brown ring complex formed in the test of the nitrate ion (NO₃⁻), we will analyze the properties of the complex and determine which statements about it are true.

### Step-by-Step Solution:

1. **Understanding the Formation of the Dark Brown Ring Complex**:
- The dark brown ring complex is formed when nitrate ions react with concentrated sulfuric acid in the presence of iron(II) sulfate (FeSO₄).

2. **Writing the Chemical Reaction**:
- The reaction can be represented as:
\[ \text{FeSO}_4 + \text{H}_2\text{SO}_4 + \text{NO}_3^- \rightarrow \text{[Fe(H}_2\text{O)}_5\text{NO]}^{2+} + \text{SO}_4^{2-} \]
- The complex formed is [Fe(H₂O)₅NO]²⁺.

3. **Analyzing the Charge and Oxidation States**:
- In the complex, iron (Fe) is coordinated with five water molecules and one nitrosyl (NO) ligand.
- The oxidation state of iron can be calculated as follows:
- Let the oxidation state of iron be \( x \).
- The nitrosyl ligand (NO) contributes +1 charge.
- The overall charge of the complex is +2.
- Therefore, the equation becomes:
\[ x + 5(0) + 1 = 2 \implies x = 1 \]
- Hence, the oxidation state of iron in this complex is +1.

4. **Color of the Complex**:
- The dark brown color of the complex is attributed to charge transfer spectra, which involves electronic transitions within the complex.

5. **Analyzing the Statements**:
- **Statement 1**: "Color is due to charge transfer spectra" - This statement is **true**.
- **Statement 2**: "Iron and anode both are positive 1 charge" - This statement is **true** as we calculated the oxidation state of iron to be +1.
- **Statement 3**: "The complex species can be represented by Fe(H₂O)₅NO" - This statement is **true** as we derived this formula.
- **Statement 4**: "Iron has +2 oxidation state" - This statement is **false** as we calculated the oxidation state to be +1.

### Conclusion:
The true statements about the dark brown ring complex are:
- The color is due to charge transfer spectra.
- Iron and the nitrosyl ligand are both positive 1 charge.
- The complex species can be represented by Fe(H₂O)₅NO.

### Final Answer:
The correct options regarding the dark brown ring complex are:
- Color is due to charge transfer spectra.
- Iron and anode both are positive 1 charge.
- The complex species can be represented by Fe(H₂O)₅NO.