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Chemistry Question on properties of d block elements

The correct order of spin-only magnetic moments among the following is : (Atomic number : Mn=25, Co=27, Ni=28, Zn=30)

A

[ZnCl4]2−>[NiCl4]2−>[CoCl4]2−>[MnCl4]2\left[ ZnCl _{4}\right]^{2-}>\left[ NiCl _{4}\right]^{2-}>\left[ CoCl _{4}\right]^{2-}>\left[ MnCl _{4}\right]^{2}

B

[CoCl4]22>[MnCl4]2−>[NiCl4]22>[ZnCl4]2−\left[ CoCl _{4}\right]^{2^{2}}>\left[ MnCl _{4}\right]^{2^{-}}>\left[ NiCl _{4}\right]^{2^{2}}>\left[ ZnCl _{4}\right]^{2-}

C

[NiCl4]2>[CoCl4]2−>[MnCl4]2>[ZnCl4]2−\left[ NiCl _{4}\right]^{2}>\left[ CoCl _{4}\right]^{2-}>\left[ MnCl _{4}\right]^{2}>\left[ ZnCl _{4}\right]^{2-}

D

[MnCl4]22>[CoCl4]2−>[NiCl4]2>[ZnCl4]2−\left[ MnCl _{4}\right]^{2^{2}}>\left[ CoCl _{4}\right]^{2-}>\left[ NiCl _{4}\right]^{2}>\left[ ZnCl _{4}\right]^{2-}

Answer

[MnCl4]22>[CoCl4]2−>[NiCl4]2>[ZnCl4]2−\left[ MnCl _{4}\right]^{2^{2}}>\left[ CoCl _{4}\right]^{2-}>\left[ NiCl _{4}\right]^{2}>\left[ ZnCl _{4}\right]^{2-}

Explanation

Solution

The spin only magnetic moment is given by μ=n(n+2)\mu=\sqrt{n(n+2)}

where nn is the number of unpaired electrons and μ\mu is the spin-only magnetic moment. The complex having higher number of unpaired electrons will have higher value of spin only magnetic moment,

In [ZnCl4]2−,Zn2+\left[ ZnCl _{4}\right]^{2-}, Zn ^{2+} has d10d^{10} electronic configuration with 0 unpaired electrons.

In [NiCl ] 2 -, Ni2Ni ^{2} thas d8d^{8} electronic configuration with 2 unpaired electrons.

In [CoCl4]2,Co2+\left[ CoCl _{4}\right]^{2}, Co ^{2+} has d7d^{7} electronic configuration with 3 unpaired electrons.

In [MnCl4F2,Mn2\left[ MnCl _{4} F ^{2}, Mn ^{2}\right. 'has d5d^{5} electronic configuration with 5 unpaired electrons. Hence, correct order is [MnCl4]2−>[CoCl4]→>[NiCl4]2−>[ZnCl4]2\left[ MnCl _{4}\right]^{2-}>\left[ CoCl _{4}\right]^{\rightarrow}>\left[ NiCl _{4}\right]^{2-}>\left[ ZnCl _{4}\right]^{2}