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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3cc050

Which of the following complexes are diamagnetic? (Cyanide is strong field; $[Co (NH X_{3}) X_{6}] X^{3 +}$ is low spin; $[Ni (CN) X_{4}] X^{2 -}$ is square planar and $[NiCl X_{4}] X^{2 -}$ is tetrahedral.)

A $[Fe (CN) X_{6}] X^{4 -}$
B $[Ni (CN) X_{4}] X^{2 -}$
C $[NiCl X_{4}] X^{2 -}$
D $[Co (NH X_{3}) X_{6}] X^{3 +}$

Answer: A, B, D

Fe(II) low spin

d^{6}

(

t_{2 g}^{6}

) has no unpaired electrons. Square planar Ni(II) has all eight electrons paired. Co(III) low spin

d^{6}

is

t_{2 g}^{6}

and diamagnetic. Tetrahedral Ni(II)

e^{4} t_{2}^{4}

has 2 unpaired electrons and is paramagnetic.

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