Iodine, I₂, reacts with thiosulfate ions, S₂O₃^2–to form iodide ions, I^–, and tetrathionate ions, S₄O₆^2–

I₂+S₂O₃^2–→2I^– + S₄O₆^2–

a. State the oxidation number of each sulfur atom in:

i. A S₂O₃^2– ion

ii. A  S₄O₆^2– ion

b. Explain in terms of electron transfer why the conversion of iodine to iodide ions is a reduction reaction.

c. When a salt containing iodide ions is warmed with concentrated sulfuric acid and MnO2, iodine is evolved.

2I^– + MnO₂ + 6H⁺ + 2SO₄^2– → I₂ + Mn²⁺ + 2HSO₄ – + 2H₂O

i. State the systematic name for MnO₂.

ii. What is the oxidation number of S in the SO₄^2–ion?

iii. Which reactant gets oxidised in this reaction? Explain your answer by using oxidation numbers.

iv. Which substance is the oxidising agent? Explain your answer.