Iron(III) catalyses the reaction between iodide and persulphate ions, in which: A. Fe3+ oxidises the iodide ion B. Fe3+…

Concept: Fe³⁺ as intermediate catalyst

The overall reaction: $2\text{I}^- + \text{S}_2\text{O}_8^{2-} \rightarrow \text{I}_2 + 2\text{SO}_4^{2-}$

Fe³⁺ acts as an intermediate catalyst in two steps:

Step 1: $\text{Fe}^{3+}$ oxidises $\text{I}^-$: $2\text{Fe}^{3+} + 2\text{I}^- \rightarrow 2\text{Fe}^{2+} + \text{I}_2 \quad \text{(A is correct)}$

Step 2: $\text{Fe}^{2+}$ reduces $\text{S}_2\text{O}_8^{2-}$ (persulphate): $2\text{Fe}^{2+} + \text{S}_2\text{O}_8^{2-} \rightarrow 2\text{Fe}^{3+} + 2\text{SO}_4^{2-} \quad \text{(D is correct)}$

Fe³⁺ is regenerated → acts as a true catalyst.

Correct statements: A and D

Answer: Option (4) — A and D only