(a) Account for the following:
(i) `Ce^(4+)` is a strong oxidising agent in aqueous solution.
(ii) Transition metals have high enthalpy of atomisation.
(iii) Mn shows maximum number of oxidation states in 3d series.
(b) Complete the following equations:
(i) `2MnO_(4)^(-)+6H^(+)+5NO_(2)^(-)to`
(ii) `Cr_(2)O_(7)^(2-)+14H^(+)+6Fe^(2+)to`

Explanation

(a) (i) In aqueous solutions `Ce^(4+)` tends to change to `Ce^(3+)` as +3 oxidation state is more stable.
Therefore `Ce^(4+)` acts as an oxidising agent.
(ii) Transition metals have a large number of unpaired electrons in their atoms. They form strong metallic bonds and therefore have a high enthalpy of atomisation.
(iii) Mn has the electronic configuration `-3d^(5)4s^(2)`. It shows oxidation states from +2 to +7. It has the maximum number of unpaired electrons.
(b) (i) `MnO_(4)^(-)+8H^(+)+5e^(-)to Mn^(2+)+4H_(2)O"]"xx2`
`(NO_(2)^(-)+H_(2)O to NO_(3)^(-)+2H^(+)+2e^(-)"]"xx5)/(2MnO_(4)^(-)+5NO_(2)^(-)+6H^(+)to 2Mn^(+)+5NO_(3)^(-)+3H_(2)O)`
(ii) `Cr_(2)O_(7)^(2-)+14H^(+)+6e^(-)to 2Cr^(3+)+7H_(2)O`
`(Fe^(2+)toFe^(3+)+e^(-)"]"xx6)/(Cr_(2)O_(7)^(2-)+6Fe^(2+)+14H^(+)to 2Cr^(3+)+6Fe^(3+)+7H_(2)O)`