Explain why
(i) `E^(@)` for `Mn^(3+)//Mn^(2+)` couple is more positive than that for `Fe^(3+)//Fe^(2+)` ?
(ii) `Ce^(3+)` can be easily oxidised to `Ce^(4+)` ?
[Atomic numbers : Mn = 25, Fe = 26 Ce = 58]

Explanation

(i) `Mn^(2+)` is more stable because of half-filled `(4s^0)5d^(5))` d-orbitals than `Mn^(3+)(4s^(0)3d^(4))` while `Fe^(3+)(4s^(0)3d^(5))` is more stable than `Fe^(2+)(4s^(0)3d^(6))` again because of half-filled d-orbitals. Therefore, `Mn^(3+)` can be easily reduced to `Mn^(2+)` whereas Fe3+ is not easily reduced to `Fe^(2+)`, rather `Fe^(2+)` is more easily oxidised to `Fe^(3+)`.
(ii) `Ce^(4+)` is more stable than `Ce^(3+)` because of stable electronic configuration and higher hydration energy of `Ce^(4+)`, hence `Ce^(3+)` is easily oxidised to `Ce^(4+)`.