Question

Why $Z{n}^{2+}$ is diamagnetic whereas $C{r}^{3+}$ is paramagnetic ?

Answer 1

${Zn}^{+2}$ has the outermost electronic configuration $3d^{10}$ and therefore it has no unpaired electron while ${Cr}^{+3}$ has the outermost elctronic configuration as $3d^3$ and therefore, it has $3$ unpaired electron.

Hence ${Zn}^{+2}$ is diamagnetic whereas ${Cr}^{+3}$ is paramagnetic.