The cell reaction Zn + Cu2+ → Zn2+ + Cu is best represented by

The correct answer is Option (2) → Zn | Zn²⁺ || Cu²⁺ | Cu

• In cell notation the anode is written on the left and the cathode on the right. A single vertical line separates a metal from its electrolyte solution, and a double vertical line stands for the salt bridge between the two solutions.

• In \( \ce{Zn + Cu^2+ -> Zn^2+ + Cu} \), zinc is oxidised and copper ions are reduced:

      Anode (left): \( \displaystyle \ce{Zn(s) -> Zn^2+(aq) + 2e^-} \)
      Cathode (right): \( \displaystyle \ce{Cu^2+(aq) + 2e^- -> Cu(s)} \)

• So the zinc half-cell, Zn | Zn²⁺, comes first and the copper half-cell, Cu²⁺ | Cu, comes after the double line: Zn | Zn²⁺ || Cu²⁺ | Cu (the Daniell cell).

Why the other options are incorrect

Option (1) Cu | Cu²⁺ || Zn²⁺ | Zn — Incorrect. It puts copper on the left as the anode, so it stands for the reverse reaction, \( \ce{Cu + Zn^2+ -> Cu^2+ + Zn} \).

Option (3) Cu²⁺ | Cu || Zn | Zn²⁺ — Incorrect. The copper half-cell is again on the left and the zinc half-cell on the right, so the cathode and anode are interchanged.

Option (4) Pt | Zn²⁺ || Pt | Cu²⁺ — Incorrect.

• Zinc and copper metals take part in the reaction and are themselves the electrodes.

• An inert Pt electrode is used only when no metal of the couple can act as the electrode, such as the hydrogen electrode.

NCERT (2026-27 edition):
2.2 Galvanic Cells – “… It is now an accepted convention that we keep the anode on the left and the cathode on the right while representing the galvanic cell. A galvanic cell is generally represented by putting a vertical line between metal and electrolyte solution and putting a double vertical line between the two electrolytes connected by a salt bridge.”