Which one of the following transition metal ions is diamagnetic?

Options

A. `Co^(2+)`
B. `Ni^(2+)`
C. `Cu^(2+)`
D. `Zn^(2+)`

Answer

To determine which transition metal ion is diamagnetic, we need to analyze the electronic configurations of the given ions and check for unpaired electrons. A diamagnetic ion has all its electrons paired, while a paramagnetic ion has one or more unpaired electrons.

### Step-by-Step Solution:

1. **Understand Diamagnetism**:
- Diamagnetic substances have all their electrons paired. This means that there are no unpaired electrons in the atom or ion.

2. **Identify the Transition Metal Ions**:
- The transition metal ions we need to analyze are Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺.

3. **Determine the Electronic Configuration of Each Ion**:
- **Co²⁺**:
- Atomic number of Co = 27.
- Ground state configuration: [Ar] 4s² 3d⁷.
- For Co²⁺, we remove 2 electrons (from 4s):
- Configuration: [Ar] 3d⁷ (which is 3d⁷).
- **Ni²⁺**:
- Atomic number of Ni = 28.
- Ground state configuration: [Ar] 4s² 3d⁸.
- For Ni²⁺, we remove 2 electrons (from 4s):
- Configuration: [Ar] 3d⁸.
- **Cu²⁺**:
- Atomic number of Cu = 29.
- Ground state configuration: [Ar] 4s² 3d¹⁰.
- For Cu²⁺, we remove 2 electrons (from 4s):
- Configuration: [Ar] 3d⁹.
- **Zn²⁺**:
- Atomic number of Zn = 30.
- Ground state configuration: [Ar] 4s² 3d¹⁰.
- For Zn²⁺, we remove 2 electrons (from 4s):
- Configuration: [Ar] 3d¹⁰.

4. **Draw Orbital Representation and Count Unpaired Electrons**:
- **Co²⁺ (3d⁷)**:
- Orbital representation: ↑↓ ↑↓ ↑ ↑ ↑
- Unpaired electrons: 3 (paramagnetic).
- **Ni²⁺ (3d⁸)**:
- Orbital representation: ↑↓ ↑↓ ↑↑ ↑
- Unpaired electrons: 2 (paramagnetic).
- **Cu²⁺ (3d⁹)**:
- Orbital representation: ↑↓ ↑↓ ↑↑ ↑ ↑
- Unpaired electrons: 1 (paramagnetic).
- **Zn²⁺ (3d¹⁰)**:
- Orbital representation: ↑↓ ↑↓ ↑↓ ↑↓ ↑↓
- Unpaired electrons: 0 (diamagnetic).

5. **Conclusion**:
- The only ion that has all paired electrons is Zn²⁺. Therefore, Zn²⁺ is the diamagnetic ion.

### Final Answer:
The transition metal ion that is diamagnetic is **Zn²⁺**.