For `M^(+2)//M` and `M^(+3)//M^(+2)` systems, the `E^(@)` values for some metals are as follows :
`Cr^(+2)//Cr=-0.9V, Cr^(+3)//Cr^(+2)=-0.4V`
`Mn^(+2)//Mn=-1.2V, Mn^(+3)//Mn^(+2)=+1.5V`
`Fe^(+2)//Fe=-0.4V, Fe^(+3)//Fe^(+2)=+0.80V`
Use this data to comment upon :
the case with which iron can be oxidised as compared to a similar process for either chromium or manganese metal.

Explanation

Lower the reduction potential or higher the oxidation potential of a species, greater the case with which its oxidation will take place. Thus, the order of tendency to undergo oxidation is `Fe lt Cr lt Mn`.
Note : Oxidation and reduction potentials have the same magnitude but opposite in sign.