Give reason for the folloiwng :
(a) `E_("value")^(@)` for `Mn^(3+)//Mn^(2+)` couple is much more positive than that of `Fe^(3+)//Fe^(2+)` couple.
(b) Iron has higher enthalpy of atomization then that of copper.
(c) `Sc^(3+)` is colourless in aqueous solution whereas `Ti^(3+)` is coloured.

Explanation

(a) `underset("(Less stable)") underset(3d^(4))(Mn^(3+)) overset(+e^(-))to underset("(More stable)")underset(3d^(5))(Mn^(2+)),underset("(More stable)")underset(3d^(5))(Fe^(3+)) overset(+e^(-))to underset("(Less stable)")underset(3d^(6))(Fe^(2+))`
Since `Mn^(3+)//Mn^(2+)` couple is more stable as compared to `Fe^(3+)//Fe^(2+)` couple, the `E_("value")^(@)` for the former is more.
(b) In case of Fe (Z=26), number of unpaired electron is more than in case of Cu(Z=29). As a result, the metallic bond in iron is stronger and it has higher enthalpy of atomisation than that of Fe.
(c) `Sc^(3+)(3d^(0))` has no unpaired electron while `Ti^(3+)(3d^(1))` has one unpaired electrons. Therefore, `Sc^(3+)` is colourless while `Ti^(3+)` is coloured in aqueous solution.