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 of the following transition metal ions is colorless, we need to analyze the electronic configurations of the given ions and check for the presence of unpaired electrons. Transition metal ions that have no unpaired electrons are typically colorless and are considered diamagnetic.

### Step-by-Step Solution:

1. **Identify the Transition Metal Ions**:
We need to evaluate the following transition metal ions: Vanadium (V²⁺), Chromium (Cr³⁺), Zinc (Zn²⁺), and Titanium (Ti³⁺).

2. **Determine the Electronic Configuration**:
- **Vanadium (V)**:
- Atomic number: 23
- Ground state configuration: [Ar] 3d³ 4s²
- For V²⁺: Remove 2 electrons (from 4s):
- Configuration: [Ar] 3d³
- **Chromium (Cr)**:
- Atomic number: 24
- Ground state configuration: [Ar] 3d⁵ 4s¹
- For Cr³⁺: Remove 3 electrons (2 from 4s and 1 from 3d):
- Configuration: [Ar] 3d³
- **Zinc (Zn)**:
- Atomic number: 30
- Ground state configuration: [Ar] 3d¹⁰ 4s²
- For Zn²⁺: Remove 2 electrons (from 4s):
- Configuration: [Ar] 3d¹⁰
- **Titanium (Ti)**:
- Atomic number: 22
- Ground state configuration: [Ar] 3d² 4s²
- For Ti³⁺: Remove 3 electrons (2 from 4s and 1 from 3d):
- Configuration: [Ar] 3d¹

3. **Count Unpaired Electrons**:
- **V²⁺ (3d³)**: 3 unpaired electrons (colored)
- **Cr³⁺ (3d³)**: 3 unpaired electrons (colored)
- **Zn²⁺ (3d¹⁰)**: 0 unpaired electrons (colorless)
- **Ti³⁺ (3d¹)**: 1 unpaired electron (colored)

4. **Conclusion**:
Among the given transition metal ions, **Zinc (Zn²⁺)** is the only ion that is colorless because it has no unpaired electrons.

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