The deep red colour of `Fe(SCN)_6^(3-)` and ` is destroyed by addition of

Options

A. `F^(-)`
B. `CN^(-)`
C. `SCN^(-)`
D. `Fe`

Explanation

To solve the question regarding the destruction of the deep red color of `Fe(SCN)6^(3-)`, we will analyze the reactions that occur when different ions are added to the solution.

### Step-by-Step Solution:

1. **Understanding the Complex**:
The complex ion `Fe(SCN)6^(3-)` is formed from iron (Fe) in the +3 oxidation state and thiocyanate ions (SCN^-). This complex is known for its deep red color due to the d-d transitions of the iron ion.

**Hint**: Recall that the color of transition metal complexes is often due to d-d transitions, which can be influenced by the ligands surrounding the metal ion.

2. **Identifying Possible Additives**:
The question mentions the addition of F^-, Ca^2+, SCN^-, and Fe^3+. We need to consider how each of these ions interacts with `Fe(SCN)6^(3-)`.

**Hint**: Think about the nature of the ligands and how they might affect the stability and color of the complex.

3. **Reaction with Fluoride Ion (F^-)**:
When fluoride ions (F^-) are added to the solution containing `Fe(SCN)6^(3-)`, they can replace the thiocyanate ions due to their stronger field strength. The reaction can be represented as:
\[ Fe(SCN)6^{3-} + 6F^- \rightarrow FeF_6^{3-} + 6SCN^- \]
The product `FeF6^(3-)` does not have a color, leading to the destruction of the deep red color of the original complex.

**Hint**: Consider how the replacement of ligands can lead to a change in color, especially when moving from a colored complex to a colorless one.

4. **Reaction with Other Ions**:
- **Calcium Ion (Ca^2+)**: Calcium does not directly react with the complex to change its color.
- **Thiocyanate Ion (SCN^-)**: Adding more SCN^- would not destroy the color; it would maintain or enhance it.
- **Iron Ion (Fe^3+)**: Adding more Fe^3+ would not destroy the color but could lead to the formation of other complexes.

**Hint**: Analyze how the addition of each ion affects the equilibrium of the complex and whether they can replace SCN^-.

5. **Conclusion**:
The addition of fluoride ions (F^-) is the most effective way to destroy the deep red color of `Fe(SCN)6^(3-)` by forming a colorless complex `FeF6^(3-)`.

**Final Answer**: The deep red color of `Fe(SCN)6^(3-)` is destroyed by the addition of **F^-**.