Question

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

• A. $\left[ ZnCl _{4}\right]^{2-}>\left[ NiCl _{4}\right]^{2-}>\left[ CoCl _{4}\right]^{2-}>\left[ MnCl _{4}\right]^{2}$
• B. $\left[ CoCl _{4}\right]^{2^{2}}>\left[ MnCl _{4}\right]^{2^{-}}>\left[ NiCl _{4}\right]^{2^{2}}>\left[ ZnCl _{4}\right]^{2-}$
• C. $\left[ NiCl _{4}\right]^{2}>\left[ CoCl _{4}\right]^{2-}>\left[ MnCl _{4}\right]^{2}>\left[ ZnCl _{4}\right]^{2-}$
• D. $\left[ MnCl _{4}\right]^{2^{2}}>\left[ CoCl _{4}\right]^{2-}>\left[ NiCl _{4}\right]^{2}>\left[ ZnCl _{4}\right]^{2-}$

Answer 1

The Correct Option is D

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

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

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

In [NiCl ] 2 -, $Ni ^{2}$ thas $d^{8}$ electronic configuration with 2 unpaired electrons.

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

In $\left[ MnCl _{4} F ^{2}, Mn ^{2}\right.$ 'has $d^{5}$ electronic configuration with 5 unpaired electrons. Hence, correct order is $\left[ MnCl _{4}\right]^{2-}>\left[ CoCl _{4}\right]^{\rightarrow}>\left[ NiCl _{4}\right]^{2-}>\left[ ZnCl _{4}\right]^{2}$