Ions of `Zn^(2+)` and `Ti^(4+)` are colourless while `Cu^(2+)` and `Ni^(2+)` are coloured. Why?

Explanation

To understand why the ions \( \text{Zn}^{2+} \) and \( \text{Ti}^{4+} \) are colorless while \( \text{Cu}^{2+} \) and \( \text{Ni}^{2+} \) are colored, we need to analyze their electronic configurations and the presence of unpaired electrons.

### Step-by-Step Solution:

1. **Identify the Electronic Configuration of Each Ion:**
- **Zinc Ion (\( \text{Zn}^{2+} \)):**
- Atomic number of Zn = 30
- Ground state configuration: \( [\text{Ar}] 3d^{10} 4s^2 \)
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