(a) Give reasons for the following :
(i) `Mn^(3+)` is a good oxidising agent.
(ii) `E(M^(2+)//M)^(@)` values are not regular for first row transition metals (3d series).
(iii) Although 'F' is more electronegative then 'O', the highest Mn fluoride is `MnF_(4)` whereas the highest oxide is `Mn_(2)O_(7)`.
Complete the following equations :
(ii) `2 CrO_(4)^(2-)+2H^(+)rarr`
(ii) `KMnO_(4)overset("heat")rarr`

Explanation

(i) `Mn^(3+)//Mn^(2+)` has large `E^(@)` (positive) value `Mn^(2+)` has half filled electronic configuration hence it is more stable then `Mn^(3+)`
(ii) `E^(@)(M^(2+)//M)` values are not regular. This can be explained due to irregular variation of ionization energies `(IE_(1) + IE_(2))` and also the sublimation energies. Stability of +2 oxidation state decreases from left to right (except Mn and Zn)
(iii) The electronic configuration in mangnese fluoride is `MnF_(4)` highest oxidation state of manages in fluoride is + 4 but highest oxidation state is oxide is + 7 in `Mn_(2)O_(7)` because oxgen can form multiple bond. Where as fluorine can form single bond with metal.
(b) (i) `2CrO_(4)^(2-)+2H^(+)rarrCr_(2)O_(7)^(2-)+H_(2)O`
(ii) (ii) `2KMnO_(4)overset("heat")rarrK_(2)MnO_(4)+MnO_(2)+O_(2)`