Stability of `Fe^(3+)` ion is greater than `Mn^(3+)` ion but less than `Cr^(3+)` - explain.
[Given : `E_(Cr^(2+)|Cr)^(0)=-0.9V, E_(Cr^(3+)|Cr^(2+))^(0)=-0.4V`
`E_(Mn^(2+)|Mn)^(0)=-1.2V, E_(Mn^(3+)|Mn^(2+))^(0)=+1.5V`
`E_(Fe^(2+)|Fe)^(0)=-0.4V, E_(Fe^(3+)|Fe^(2+))^(0)=+0.8V`]

Explanation

Higher the standard reduction potential of a system, easier it is to reduce the oxidised form. Now, according to the given data, `E_(Mn^(3+)|Mn^(2+))^(0)gt E_(Fe^(3+)|Fe^(2+))^(0)gt E_(Cr^(3+)|Cr^(2+))^(0)`.
Therefore, the ease of reduction of the trivalent ions follows the sequence : `Mn^(3+)gt Fe^(3+)gt Cr^(3+)`.
Thus, in acid medium, stability of `Fe^(3+)` ion is more than `Mn^(3+)` ion but less than `Cr^(3+)` ion.