Which of the following transition metal ions is colourless ?

Options

A. `V^(2+)`
B. `Cr^(3+)`
C. `Zn^(2+)`
D. `Ti^(3+)`

Explanation

To determine which transition metal ion is colorless, we need to analyze the electronic configurations of the given ions and check for the presence of unpaired electrons. Transition metal ions are typically colored due to the presence of unpaired electrons in their d-orbitals. If an ion has no unpaired electrons, it will be colorless.

### Step-by-Step Solution:

1. **Understand the Requirement for Color**:
- Transition metal ions are colored if they have unpaired electrons. Conversely, if they have all paired electrons, they are colorless.

2. **Analyze Each Ion**:
- **Vanadium (V²⁺)**:
- Original electronic configuration: [Ar] 3d³ 4s²
- For V²⁺, we remove two electrons (from 4s and one from 3d):
- Configuration: 3d³
- Unpaired electrons: 3 (hence, colored)

- **Chromium (Cr³⁺)**:
- Original electronic configuration: [Ar] 3d⁵ 4s¹
- For Cr³⁺, we remove three electrons (two from 4s and one from 3d):
- Configuration: 3d³
- Unpaired electrons: 3 (hence, colored)

- **Zinc (Zn²⁺)**:
- Original electronic configuration: [Ar] 3d¹⁰ 4s²
- For Zn²⁺, we remove two electrons (from 4s):
- Configuration: 3d¹⁰
- Unpaired electrons: 0 (hence, colorless)

- **Titanium (Ti³⁺)**:
- Original electronic configuration: [Ar] 3d² 4s²
- For Ti³⁺, we remove three electrons (two from 4s and one from 3d):
- Configuration: 3d¹
- Unpaired electrons: 1 (hence, colored)

3. **Conclusion**:
- The only ion that has no unpaired electrons is **Zinc (Zn²⁺)**, which is therefore colorless.

### Final Answer:
**Zinc (Zn²⁺) is the colorless transition metal ion.**

---