${\left[\mathrm{M}\mathrm{n}{\mathrm{O}}_4\right]}^{2-};$ Mn is in + 6 oxidation state. Electronic configuration is ${\left[\mathrm{A}\mathrm{r}\right]}^{18}3{\mathrm{d}}^{1}4{\mathrm{s}}^0$ . As it contains one unpaired electron it is paramagnetic and green coloured because of d-d transition in visible region. ${\left[\mathrm{T}\mathrm{i}\mathrm{C}{\mathrm{l}}_6\right]}^{2-},{\left[\mathrm{V}{\mathrm{O}}_4\right]}^{3-}$ and $\mathrm{C}\mathrm{r}{\mathrm{O}}_2\mathrm{C}{\mathrm{l}}_2$ are diamagnetic.