Iron (III) catalyses the reaction between iodide and persulphate ions, in which 

A. $$Fe^{3+}$$ oxidises the iodide ion 

B. $$Fe^{3+}$$ oxidises the persulphate ion 

C. $$Fe^{2+}$$ reduces the iodide ion 

D. $$Fe^{2+}$$ reduces the persulphate ion. 

Choose the most appropriate answer from the options given below:

Iron(III) catalyses the reaction between iodide and persulphate ions. Identify the correct mechanism.

The overall reaction is $$2I^- + S_2O_8^{2-} \rightarrow I_2 + 2SO_4^{2-}$$.

In the catalytic cycle of Fe³⁺/Fe²⁺, Fe³⁺ oxidizes I⁻: $$2Fe^{3+} + 2I^- \rightarrow 2Fe^{2+} + I_2$$. Fe²⁺ is then re-oxidized by persulphate (Fe²⁺ reduces persulphate): $$2Fe^{2+} + S_2O_8^{2-} \rightarrow 2Fe^{3+} + 2SO_4^{2-}$$.

So: A (Fe³⁺ oxidises iodide) and D (Fe²⁺ reduces persulphate) are correct.

The correct answer is Option (4): A and D only.