Give reasons for the following:
(a) Transition metals have high enthalpies of atomisation,
(b) Among the lanthanoids, Ce (III) is easily oxidised to Ce (IV).
(c) `Fe^(3+) |Fe^(2+)` redox couple has less positive electrode potential than `Mn^(3+)|Mn^(2+)` couple.
(d) Copper (I) has `d^(10)` configuration, while copper (II) has `d^(9)` configuration, still copper (II) is more stable in aqueous solution than copper (I).
(e) The second and third transition series elements have almost similar atomic radii.

Explanation

(a) Due to the presence of unpaired electrons in d-orbitals, there is strong metallic bonding. A large amount of energy is needed to separate them into atoms.
(b) `Ce^(4+)` has inert gas stable configuration. That is why Ce (III) is readily oxidised to Ce (IV).
(c) `Mn^(2+)` is more stable than `Mn^(3+)` due to half-filled electronic configuration. The reaction `Mn^(3+)+e^(-)toMn^(2+)` takes place more conveniently compared to the reaction `Fe^(3+)+e^(-)toFe^(2+)`.
(d) As there are no vacant d-orbitals in Cu (I) water cannot form coordinate bond whereas Cu (II) can form coordinate bonds with water. Hydration energy provides stability to Cu (II) in aqueous solution.
(e) As the electrons are being added in the inner shell, atomic radii do not change significantly in the second and third transition series.