In the change `[Cu(H_(2)O)_(6)]^(2+)overset(HCl)rarr [CuCl(H_(2)O)_(5)]^(+)`, the colour changes from

Options

A. blue to green
B. blue to pink
C. pink to green
D. pink to blue

Answer

To solve the question regarding the color change in the complex ion transformation from \([Cu(H_2O)_6]^{2+}\) to \([CuCl(H_2O)_5]^{+}\) when treated with HCl, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Initial Complex**: The initial complex is \([Cu(H_2O)_6]^{2+}\). This complex is formed with copper in the +2 oxidation state coordinated with six water molecules.

2. **Identify the Final Complex**: The final complex after the addition of HCl is \([CuCl(H_2O)_5]^{+}\). In this complex, one of the water molecules is replaced by a chloride ion (Cl⁻).

3. **Understand the Color of the Complexes**:
- The complex \([Cu(H_2O)_6]^{2+}\) is known to be blue in color. This is due to the presence of water as a ligand, which affects the d-orbitals of copper and results in the absorption of specific wavelengths of light.
- The complex \([CuCl(H_2O)_5]^{+}\) is typically green in color. The presence of chloride ions as ligands alters the electronic environment around the copper ion, leading to a different color.

4. **Determine the Color Change**: When the reaction occurs, the color changes from blue (for \([Cu(H_2O)_6]^{2+}\)) to green (for \([CuCl(H_2O)_5]^{+}\)).

5. **Conclusion**: Therefore, the color change observed during this transformation is from blue to green.

### Final Answer:
The color changes from blue to green.

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