Question

Which has the stable electronic configuration? Ni²⁺ or Fe³⁺.

Answer 1

electronic configuration of Ni²⁺ (26e⁻) : [Ar]4s⁰3d⁸
There are two unpaired electrons in Ni²⁺ . Means two orbitals are incomete .

now, electronic configuration of Fe³⁺ (23e⁻) : [Ar]4s⁰3d⁵
There are five unpaired electrons . Means five orbitals are incomete. But we know, d - subshell have only five orbitals . Here in case of Fe³⁺ , all five electrons are configure in each orbitals. Means Fe³⁺ has half filled configuration . And we know, stability of half filled or full filled greater than other configuration.
So, Fe³⁺ k more stable than Ni²⁺

Hence, Fe³⁺ is more stable than Ni²⁺.