Answer: 1.
- A 2
- B 1
- C 4
- D 6
Correct answer: B. 1
Explanation: In S₂O₃²⁻: S is +2. In S₄O₆²⁻: S is +2.5. Each Na₂S₂O₃ loses 0.5 electrons (per S₂O₃²⁻ unit, 2 S atoms each go from +2 to +2.5 = 1 electron lost total per mole). n-factor = 1.
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.