Redox roles in thiosulfate-iodine reaction Steps:

• Calculate oxidation state of S in S₂O₃²⁻: 2S + 3(-2) = -2, so 2S = +4, average +2 per S.
• Calculate oxidation state of S in S₄O₆²⁻: 4S + 6(-2) = -2, so 4S = +10, average +2.5 per S (actual: two S at 0, two at +5).
• Oxidation state increases from +2 to +2.5, indicating loss of electrons.
• Thus, S₂O₃²⁻ loses electrons and is oxidized (I₂ gains electrons, reduced).

Why D is correct:

• Oxidized substances lose electrons, matching the increase in S oxidation state per IUPAC definition.

Why the others are wrong:

• A: Oxidized ions lose, not gain, electrons.
• B: Thiosulfate loses electrons, so not reduced.
• C: Thiosulfate is oxidized, not reduced by gaining electrons.

Final answer: D