Answer: +5.
- A +3
- B +5
- C +4
- D -3
Correct answer: B. +5
Explanation: In H₃PO₄: 3(+1) + P + 4(-2) = 0. P = 8 - 3 = +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.