The geometry and magnetic behaviour of the complex [Ni(CO)₄] are

• Square planar geometry and diamagnetic

• Tetrahedral geometry and diamagnetic

• Tetrahedral geometry and paramagnetic

• Square planar geometry and paramagnetic

B.

Tetrahedral geometry and diamagnetic

Ni(28) : [Ar]3d⁸ 4s2
∵CO is a strong field ligand, so unpaired electrons get paired. Hence, the configuration would be.

For, four ‘CO’-ligands hybridisation would be sp³ and thus the complex would be diamagnetic and of tetrahedral geometry.