How would you account for the following?
(i)The atomic radii of the metals of the third (5d) series of transition elements are virtually the same as those of the corresponding members of the second (4d) series.
(ii)The `E^(@)` value for the `Mn^(3+)//Mn^(2+)` couple is much more positive than that for `Cr^(3+)//Cr^(2+)` couple or `Fe^(3+)//Fe^(2+)` couple.
(iii)The highest oxidation state of a metal is exhibited in its oxide or fluoride.

Explanation

(i) Due to Lanthanoid Contraction.
(ii) Due to stable-filled `3d^(5)` configuration of `Mn(2+)` or 3rd ionisation enthalpy of Mn. (iii) Because oxygen or Fluorine is highly electronegative element and small size.