(a) Transition metals can act as catalysts because these can change their oxidation state. How does Fe(III) catalyse the reaction between iodide and persulphate ions ?
(b) Mention any three processes where transition metals act as catalysts.

Explanation

(a) Reaction between iodide and persulphate ions is :
`2I^(-)+S_(2)O_(8)^(2-)overset(Fe(III))toI_(2)+2SO_(4)^(2-)`
Role of Fe(III) ions :
`2Fe^(3+)+2I^(-)to2Fe^(3+)+I_(2)`
`2Fe^(2+)+S_(2)O_(8)^(2-)to2Fe^(3+)+2SO_(4)^(2-)`
(b) (i) Vanadium (V) oxide in contact process for oxidation of `SO_(2)` to `SO_(3)`.
(ii) Finely divided iron in Haber.s process in conversion of `N_(2)` and `H_(2)` to `NH_(3)`.
(iii) `MnO_(2)` in preparation of oxygen from `KCIO_(3)`.