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 , square planar
B. two, square planar
C. one, tetrahedral
D. two, terahedral.