In the reaction: I 2 + 2S 2 O 3 2- → 2I- + S 4 O 6 2- , the oxidation state of sulphur in S 4 O 6 2- is:

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In the reaction: I2 + 2S2O32- → 2I- + S4O62-, the oxidation state of sulphur in S4O62- is:

Answer: +2.5.

A +4
B +2.5
C +6
D 0

Correct answer: B. +2.5

Explanation: In S₄O₆²⁻: 4S + 6(-2) = -2. 4S = +10. S = +2.5. In S₂O₃²⁻: 2S + 3(-2) = -2; 2S = +4; S = +2. Sulphur is oxidised from +2 to +2.5.

Electron transfer in a redox reaction: zinc loses electrons (oxidised, acts as reducing agent) and copper(II) ions gain those same electrons (reduced, acts as oxidising agent).

Concept context

Master electron transfer in chemistry: assign oxidation states, balance half-reactions, identify oxidising and reducing agents, and connect redox to everyday reactions.

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In the reaction: I<sub>2</sub> + 2S<sub>2</sub>O<sub>3</sub><sup>2-</sup> → 2I- + S<sub>4</sub>O<sub>6</sub><sup>2-</sup>, the oxidation state of sulphur in S<sub>4</sub>O<sub>6</sub><sup>2-</sup> is:

Concept context

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