Question

For which of the following $d^n$ configuration of octahedral complex(ex), cannot exist in both high spin and low spin forms?

• A. $d^3$
• B. $d^5$
• C. $d^6$
• D. $d^8$

Answer 1

Answer: (A), (D)

The correct options are
A $d^3$
D $d^8$

When the outer electronic configuration of the central metal ion in the complex is $d^1$ to $d^3$, the complex is inner orbital complex.
This is irrespective of the strength of the ligand field.
When the outer electronic configuration of the central metal ion in the complex is $d^8$ to $d^{10}$, the complex is outer orbital complex.
This is irrespective of the strength of the ligand field.
Thus, $d^3$ and $d^8$ configuration of octahedral complex(es), cannot exist in both high spin and low spin forms.