Answer: PH3.
- A PH3
- B P2O5
- C P4
- D H3PO2
Correct answer: A. PH3
Explanation: H₃PO₃ has P in +3 oxidation state. On heating: 4H₃PO₃ → 3H₃PO₄ + PH₃. P goes from +3 to +5 (in H₃PO₄, oxidised) and +3 to -3 (in PH₃, reduced). This is disproportionation.
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.