Nickel (Z = 28) combines with a uninegative monodentate ligand X– to form a paramagnetic complex [NiX4]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.
