Giving reasons indicate which one of the following would be coloured ?
`Cu^+ , V^(2+), Sc^(3+), Ni^(2+)` (At. no. of Cu = 29, V = 23, Sc = 21, Ni = 28)

Explanation

To determine which of the ions \( \text{Cu}^+, \text{V}^{2+}, \text{Sc}^{3+}, \text{Ni}^{2+} \) is colored, we need to analyze their electronic configurations and the presence of unpaired electrons in their d-orbitals.

### Step-by-Step Solution:

1. **Copper Ion (\( \text{Cu}^+ \))**:
- Atomic number of Cu = 29.
- Electronic configuration of Cu: \( [\text{Ar}] 3d^{10} 4s^1 \).
- For \( \text{Cu}^+ \), we remove one electron from the 4s orbital:
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