(a) In the titration of `FeSO_(4)` with `KMnO_(4)` in the acidic medium, why is dil. `H_(2)SO_(4)` used instead of dil. HCI ?
(b) Give reasons :
(i) Among transition metals, the highest oxidation state is exhibited in oxoanions of a metal.
(ii) `Ce^(4+)` is used as an oxidising agent in volumetric analysis.
(iii) Transition metals form a number of interstitial compounds.
(iv) `Zn^(2+)` salts are white while `Cu^(2+)` salts are blue.

Explanation

(a) HCl gets oxidised to `Cl_(2)` by `KMnO_(4)` whereas `H_(2)SO_(4)` does not.
(b) (i) Metal oxoanion may be represented as `MO_(x)^(y-)`
where y ranges between 1 to 2 and x ranges between 2 to 4.
On calculation of oxidation state of the metal in oxoanion, we find that it is the maximum.
(ii) `Ce^(4+)` can gain an electron and, therefore, it acts as an oxidising agent.
`Ce^(4+)+e^(-)toCe^(3+)`
(iii) These elements have voids in which small atoms like C, B can fit tightly to give interstitial compounds.
(iv) `Zn^(2+)` does not have vacant d-orbitals or unpaired electrons in d-orbital. `Cu^(2+)` has one unpaired electron and vacant d-orbitals.