With the help of Valence Bond theory account for hybridisation, geometry and magnetic property of `[Ni(CN)_(4)]^(2-)` complex ion `[Z" for "Ni=28]`

Explanation

Electronic configuration of `Ni^(2+) = [Ar]3d^(8) 4s^(0)`

One 3d, one 4s and two 4p orbitals undergoes `dsp^2` hybridization to give four equivalent vacant hybrid orbitals .
These four hybrid orbitals are occupied by four lone pairs of electrons from four `CN^(-)` ligands to form `[Ni(CN)_(4)]^(2-)`

Since the hybridization is `dsp^2`, the geometry is Square planar.
The complex is diamagnetic due to the absence of unpaired electrons.