Jahn - Teller effect is not observed in high spin complexes of
a.`d^(7)`
b.`d^(8)`
c.`d^(4)`
d.`d^(9)`

Options

A. `d^(7)`
B. `d^(8)`
C. `d^(4)`
D. `d^(9)`

Explanation

To solve the question regarding the Jahn-Teller effect and its relation to high spin complexes, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Jahn-Teller Effect**:
- The Jahn-Teller effect describes the geometric distortion of molecules or ions that occurs when they have degenerate electronic states. This distortion lowers the overall energy of the system.

2. **Identify High Spin Complexes**:
- High spin complexes are those where the electrons are arranged to maximize the number of unpaired electrons. This typically occurs in transition metal complexes with weak field ligands.

3. **Determine Electronic Configurations**:
- For transition metals, the electronic configurations can be represented in terms of d-electrons. The configurations of interest here are:
- d⁷
- d⁸
- d⁴
- d⁹

4. **Analyze Each Configuration**:
- **d⁷**: High spin d⁷ complexes can exhibit Jahn-Teller distortion (e.g., in Co²⁺).
- **d⁸**: High spin d⁸ complexes do not exhibit Jahn-Teller distortion (e.g., Ni²⁺).
- **d⁴**: High spin d⁴ complexes can exhibit Jahn-Teller distortion (e.g., Cr³⁺).
- **d⁹**: High spin d⁹ complexes can also exhibit Jahn-Teller distortion (e.g., Cu²⁺).

5. **Conclusion**:
- Based on the analysis, the Jahn-Teller effect is not observed in high spin complexes of **d⁸**. Therefore, the correct answer is option **b**.

### Final Answer:
**b. d⁸**