If the radius of  ${\mathrm{Fe}}^{++}\mathrm{is} 0.76 \stackrel{°}{\mathrm{A}}$; the radius of  ${\mathrm{Fe}}^{+++}\mathrm{is}$

If the ion has more positive charge then its size becomes small.

${\mathrm{Fe}}^{+2},\mathrm{r}=0.76 \stackrel{°}{\mathrm{A} } \mathrm{and} {\mathrm{Fe}}^{+3},\mathrm{r}=0.64\stackrel{°}{\mathrm{A} }$

$\therefore {\mathrm{Fe}}^{+2} \mathrm{has} \mathrm{more} \mathrm{size} \mathrm{than} {\mathrm{Fe}}^{+3}\mathrm{so}, {\mathrm{Fe}}^{+2}>{\mathrm{Fe}}^{+3}$