Which of the following ions are colourless ?

Options

A. `Ti^(3+)`
B. `Cu^(2+)`
C. `Cd^(2+)`
D. `Sc^(3+)`

Explanation

To determine which of the given ions are colorless, we need to analyze the electronic configurations of each ion and check for the presence of unpaired electrons. An ion is colorless if it has no unpaired electrons.

### Step-by-Step Solution:

1. **Identify the Ions:**
The ions we need to analyze are:
- A) Titanium +3 (Ti³⁺)
- B) Copper +2 (Cu²⁺)
- C) Cadmium +2 (Cd²⁺)
- D) Cadmium +3 (Cd³⁺)

2. **Determine the Electronic Configuration:**
- **Titanium (Ti):**
- Atomic Number: 22
- Ground State Configuration: Argon (Ar) 3d² 4s²
- For Ti³⁺: Remove 3 electrons (2 from 4s and 1 from 3d)
- Configuration: Ar 3d¹ (1 unpaired electron)

- **Copper (Cu):**
- Atomic Number: 29
- Ground State Configuration: Argon (Ar) 3d¹⁰ 4s¹
- For Cu²⁺: Remove 2 electrons (1 from 4s and 1 from 3d)
- Configuration: Ar 3d⁹ (1 unpaired electron)

- **Cadmium (Cd):**
- Atomic Number: 48
- Ground State Configuration: Krypton (Kr) 4d¹⁰ 5s²
- For Cd²⁺: Remove 2 electrons (2 from 5s)
- Configuration: Kr 4d¹⁰ (no unpaired electrons)

- **Cadmium +3 (Cd³⁺):**
- For Cd³⁺: Remove 3 electrons (2 from 5s and 1 from 4d)
- Configuration: Kr 4d⁹ (1 unpaired electron)

3. **Analyze the Number of Unpaired Electrons:**
- **Ti³⁺:** 1 unpaired electron (colored)
- **Cu²⁺:** 1 unpaired electron (colored)
- **Cd²⁺:** 0 unpaired electrons (colorless)
- **Cd³⁺:** 1 unpaired electron (colored)

4. **Conclusion:**
The ions that are colorless are:
- C) Cadmium +2 (Cd²⁺)

### Final Answer:
The colorless ion among the options is **Cadmium +2 (Cd²⁺)**.