When aqueous solution of potassium fluoride is added to the blue coloured aqueous `CuSO_(4)` solution , a green precipitate is formed . This observation can be explained as follows .

Options

A. On adding `KF , H_(2)O` being weak field ligand is replaced by `F^(-)` ions forming `[CuF_(4)]^(2-)` which is green in colour .
B. Potassium is coordinated to `[Cu(H_(2)O)_(4)]^(2+)` ion present in `CuSO_(4)` and gives green colour .
C. On adding `KF , Cu^(2+)` are replaced by `K^(+)` forming a green complex .
D. Blue colour of `CuSO_(4)` and yellow colour of KF form green colour on mixing .

Explanation

To explain the observation that a green precipitate is formed when an aqueous solution of potassium fluoride (KF) is added to a blue-colored aqueous solution of copper sulfate (CuSO₄), we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Components:**
- We have two solutions: potassium fluoride (KF) and copper sulfate (CuSO₄).
- CuSO₄ in aqueous solution is blue due to the presence of copper(II) ions (Cu²⁺).

2. **Understand the Role of Water:**
- In aqueous solution, CuSO₄ dissociates into Cu²⁺ and SO₄²⁻ ions.
- The copper(II) ions are surrounded by water molecules, forming a complex called tetra-aqua copper(II) [Cu(H₂O)₄]²⁺, which is blue in color.

3. **Introduce Potassium Fluoride:**
- When potassium fluoride is added to this solution, the fluoride ions (F⁻) from KF act as ligands.
- Fluoride is a stronger ligand compared to water.

4. **Ligand Exchange Reaction:**
- Due to the stronger ligand nature of fluoride ions, they can replace the water molecules in the tetra-aqua complex.
- The reaction can be represented as:
\[ [Cu(H₂O)₄]^{2+} + 4F^{-} \rightarrow [CuF₄]^{2-} + 4H₂O \]
- This results in the formation of the tetrafluorocuprate(II) complex, [CuF₄]²⁻.

5. **Color Change:**
- The tetrafluorocuprate(II) complex [CuF₄]²⁻ is green in color.
- Thus, the addition of KF leads to a color change from blue (due to Cu²⁺ in water) to green (due to [CuF₄]²⁻).

6. **Conclusion:**
- The formation of the green precipitate can be attributed to the ligand exchange where water is replaced by fluoride ions, resulting in a new complex that exhibits a different color.