How would you account for the following: The ${\mathrm{d}}^1$ configuration is very unstable in ions.

Give examples and suggest reasons for the following feature of the transition metal in chemistry.

A transition metal exhibits the highest oxidation state in oxides and fluorides.

The ${\mathrm{E}}^{\circ }$ value with respect of electrodes of chromium $(Z = 24)$, manganese ($Z = 25$), and iron ($\mathrm{Z} =26$) are  ${\mathrm{Cr}}^{3+}/{\mathrm{Cr}}^{2+} =- 0.4 \mathrm{V}$, ${\mathrm{Mn}}^{3+}/{\mathrm{Mn}}^{2+} = 1.5 \mathrm{V}$, ${\mathrm{Fe}}^{3+}/ {\mathrm{Fe}}^{2+} =+ 0.8 \mathrm{V}$.

On the basis of the above information, compare the feasibilities of further oxidation of their $+2$ oxidation state.