Each of the following complex ions is either tetrahedral or square planar. On the basis of the number of unpaired electrons (given in parentheses) decide which is the correct geometry. Explain your answers, using valence bond theory telling what types of hybrid orbitals are being used by the metal ion in the complex.
a. Pt(NH3)2(NO2)2^2+ (2)
b. MnCl4^-2 (5)
c. NiCl4^-2 (2)
d. AuF4^- (0)