Answer: Persistent pale pink colour of excess KMnO 4 (self-indicator).
- A The pale yellow-brown colour of the Fe<sup>3+</sup> product appearing suddenly at the endpoint
- B Persistent pale pink colour of excess KMnO<sub>4</sub> (self-indicator)
- C Addition of a starch indicator that turns blue-black at the endpoint
- D A sharp change in the measured pH of the titration mixture
Correct answer: B. Persistent pale pink colour of excess KMnO<sub>4</sub> (self-indicator)
Explanation: KMnO₄ is itself a self-indicator: MnO₄⁻ is deep purple; Mn²⁺ (product) is nearly colourless. At the end point, a single excess drop of KMnO₄ imparts a persistent pale pink/purple colour.
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.