Explain on the basis of valence bond theory that `[Ni(CN)_(4)]^(2-)` ion with square planar structure is diamagnetic and the `[NiCl_(4)]^(2-)` ion with tetrahedral geometry is paramagnetic.

Explanation

Outer configuration of `""_(28)Ni` atom =

(`CN^(-)` being strong field ligand paired up the d-electrons of metal atom.)

The complex ion is diamagnetic in nature as it has no unpaired electrons
Outer configuration of `""_(28)Ni` atom =

(`Cl^(-)` being weak field ligand, cannot cause pairing.)

`[NiCl_(4)]^(2-)` ion is paramagnetic in nature as it has two unpaired electrons.