Question

# Among the following which one has the highest paramagnetism?$\left[\mathrm{Cr}{\left({\mathrm{H}}_{2}\mathrm{O}\right)}_{6}{\right]}^{3+}$$\left[\mathrm{Fe}{\left({\mathrm{H}}_{2}\mathrm{O}\right)}_{6}{\right]}^{2+}$$\left[\mathrm{Cu}{\left({\mathrm{H}}_{2}\mathrm{O}\right)}_{6}{\right]}^{2+}$$\left[\mathrm{Zn}{\left({\mathrm{H}}_{2}\mathrm{O}\right)}_{6}{\right]}^{2+}$

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Solution

## The correct option is B $\left[\mathrm{Fe}{\left({\mathrm{H}}_{2}\mathrm{O}\right)}_{6}{\right]}^{2+}$The explanation for the correct option(B) $\mathbf{\left[}\mathbf{Fe}{\mathbf{\left(}{\mathbf{H}}_{\mathbf{2}}\mathbf{O}\mathbf{\right)}}_{\mathbf{6}}{\mathbf{\right]}}^{\mathbf{2}\mathbf{+}}$ParamagnetismParamagnetism is the ability of certain materials to be weakly attracted to the magnetic field.Paramagnetism is exhibited by molecules containing unpaired electrons.The paramagnetism property of a complex increases with the larger number of unpaired electrons.The electronic configuration of ${\mathrm{Fe}}^{2+}$ is $\left[\mathrm{Ar}\right]3{\mathrm{d}}^{6}$${\mathrm{H}}_{2}\mathrm{O}$ is a weak field ligand it does not pair up unpaired electrons.The number of unpaired electrons in $\left[\mathrm{Fe}{\left({\mathrm{H}}_{2}\mathrm{O}\right)}_{6}{\right]}^{2+}$ is $4$As the number of unpaired electrons is higher, the paramagnetic property of the complex is also higher.Hence Option (B) $\mathbf{\left[}\mathbf{Fe}{\mathbf{\left(}{\mathbf{H}}_{\mathbf{2}}\mathbf{O}\mathbf{\right)}}_{\mathbf{6}}{\mathbf{\right]}}^{\mathbf{2}\mathbf{+}}$is correctThe explanation for the incorrect options(A) $\mathbf{\left[}\mathbf{Cr}{\mathbf{\left(}{\mathbf{H}}_{\mathbf{2}}\mathbf{O}\mathbf{\right)}}_{\mathbf{6}}{\mathbf{\right]}}^{\mathbf{3}\mathbf{+}}$The electronic configuration of ${\mathrm{Cr}}^{3+}$ is $\left[\mathrm{Ar}\right]3{\mathrm{d}}^{3}$${\mathrm{H}}_{2}\mathrm{O}$ is a weak field ligand it does not pair up unpaired electrons.The number of unpaired electrons in $\left[\mathrm{Cr}{\left({\mathrm{H}}_{2}\mathrm{O}\right)}_{6}{\right]}^{3+}$ is $3$As the number of unpaired electrons is lower the paramagnetism property of the complex is also lower.(C) $\mathbf{\left[}\mathbf{Cu}{\mathbf{\left(}{\mathbf{H}}_{\mathbf{2}}\mathbf{O}\mathbf{\right)}}_{\mathbf{6}}{\mathbf{\right]}}^{\mathbf{2}\mathbf{+}}$The electronic configuration of ${\mathrm{Cu}}^{2+}$ is $\left[\mathrm{Ar}\right]3{\mathrm{d}}^{9}$${\mathrm{H}}_{2}\mathrm{O}$ is a weak field ligand it does not pair up unpaired electrons.The number of unpaired electrons in $\left[\mathrm{Cu}{\left({\mathrm{H}}_{2}\mathrm{O}\right)}_{6}{\right]}^{2+}$ is $1$As the number of unpaired electrons is lower the paramagnetism property of the complex is also lower.(D) $\mathbf{\left[}\mathbf{Zn}{\mathbf{\left(}{\mathbf{H}}_{\mathbf{2}}\mathbf{O}\mathbf{\right)}}_{\mathbf{6}}{\mathbf{\right]}}^{\mathbf{2}\mathbf{+}}$The electronic configuration of ${\mathrm{Zn}}^{2+}$ is $\left[\mathrm{Ar}\right]3{\mathrm{d}}^{10}$${\mathrm{H}}_{2}\mathrm{O}$ is a weak field ligand it does not pair up unpaired electrons.The number of unpaired electrons in $\left[\mathrm{Zn}{\left({\mathrm{H}}_{2}\mathrm{O}\right)}_{6}{\right]}^{2+}$ is $0$There are no unpaired electrons. Hence this complex is diamagneticTherefore, Option (B) $\mathbf{\left[}\mathbf{Fe}{\mathbf{\left(}{\mathbf{H}}_{\mathbf{2}}\mathbf{O}\mathbf{\right)}}_{\mathbf{6}}{\mathbf{\right]}}^{\mathbf{2}\mathbf{+}}$ is correct

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