Which among the following is most paramagnetic?

Question

Aicharya · Accepted Answer

Paramagnetic character is based upon the presence of unpaired electrons in $d$-subshell. In these complex ions. (a) In $\left[\mathrm{Cr}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{3+}$, $\mathrm{Cr}$ is present as $\mathrm{Cr}^{3+}($ Oxidation number $=+3)$ $\mathrm{Cr}^{3+}=1 s^2 2 s^2 2 p^6 3 s^2 3 p^6 3 d^3$

(b) In $\left[\mathrm{Fe}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{2+}, \mathrm{Fe}$ is present as $ \mathrm{Fe}^{2+}=1 s^2 2 s^2 2 p^6 3 s^2 3 p^6 3 d^6 $

(c) In $\left[\mathrm{Cu}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{2+}, \mathrm{Cu}$ is present as $\mathrm{Cu}^{2+}$ $ \mathrm{Cu}^{2+}=1 s^2 2 s^2 2 p^6 3 s^2 3 p^6 3 d^9 $

(d) $\mathrm{In}\left[\mathrm{Zn}\left(\mathrm{H}_2 \mathrm{O}\right)_2\right]^{2+}, \mathrm{Zn}$ is present as $\mathrm{Zn}^{2+}=1 s^2 2 s^2 2 p^6 3 s^2 3 p^6 3 d^{10}$

In complex (a), (b) and (c) have unpaired electrons, so they show property of paramagnetism. Paramangetic character $\propto$ Number of unpaired electron. So, paramagnetic character is maximum in $\left[\mathrm{Fe}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{2+}$

Which among the following is most paramagnetic?

Solution