Question

Nickel `(Z=28)` combines with a uninegative monodentate ligand `X^(-)` to form a paramagnetic complex `[NiX_4]^(2-)`. The number of unpaired electron(s) in the nickel and geometry of this complex ion are, respectively:
A. One, tetrahedral
B. Two, tetrahedral
C. One, square planar
D. Two , square planar

Answer 1

Correct Answer - B
Oxidation state of nickel in `[NiX_(4)]^(2-)` is `+2`
`Ni^(2+)=3d^(8)4s^(0)`
Since the complex `[NiX_(4)]^(2-)` is paramagnetic . So, the ligand must be unable to induce pairing in d-orbitals and its configuration should be

To accomodate four ligands in coordination sphere the hybridization that could have occured should be `sp^(3)`
Therefore, there are two unpaired electrons with tetrahedral geometry of complex.