A compound of formula $MCl X_{2} (NH X_{3}) X_{2}$ is diamagnetic and exists as two distinct isomers with different dipole moments. Which metal ion and geometry fit these facts?

Answer: C

Two isomers of

MA X_{2} B X_{2}

require square planar geometry (cis and trans); a tetrahedral

MA X_{2} B X_{2}

has only one form. Square planar needs

d^{8}

with pairing, so

Pt X^{2 +}

(

5 d^{8}

d s p^{2}

) fits and is diamagnetic. Tetrahedral

Zn X^{2 +}

is diamagnetic but has one isomer; tetrahedral

Ni X^{2 +}

and

Co X^{2 +}

are paramagnetic with one isomer.