Answer: ClO 3 −.
- A ClO<sup>−</sup>
- B ClO<sub>3</sub><sup>−</sup>
- C ClO<sub>2</sub><sup>−</sup>
- D ClO<sub>4</sub><sup>−</sup>
Correct answer: B. ClO<sub>3</sub><sup>−</sup>
Explanation: In ClO<sub>3</sub><sup>−</sup>: Cl + 3(−2) = −1 gives Cl = +5 (ClO<sup>−</sup> is +1, ClO<sub>2</sub><sup>−</sup> is +3, ClO<sub>4</sub><sup>−</sup> is +7).
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.