The correct cell representation for the following reaction is
\( Mg(s) +2Ag^+ (0.0001 M) → Mg^{2+} (0.130 M) +2Ag(s) \)
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → \( Mg(s) | Mg^{2+} (0.130M) || Ag^+ (0.0001M) | Ag(s) \)
A galvanic cell is written by convention with the anode on the left and the cathode on the right. A single vertical line marks a boundary between phases (metal and its solution), and a double vertical line stands for the salt bridge. Concentrations of the ions are written in brackets.
In the reaction, Mg is oxidised and \( \ce{Ag+} \) is reduced:
\( \displaystyle \text{Anode:}\quad \ce{Mg(s) -> Mg^2+(0.130\,M) + 2e-} \)
\( \displaystyle \text{Cathode:}\quad \ce{2Ag+(0.0001\,M) + 2e- -> 2Ag(s)} \)
So the Mg electrode goes on the left, written metal first, and the Ag electrode on the right, written ion first:
\( \displaystyle \ce{Mg(s)}\,|\,\ce{Mg^2+}(0.130\,\mathrm{M})\,||\,\ce{Ag+}(0.0001\,\mathrm{M})\,|\,\ce{Ag(s)} \)
This is Option (1).
Why the other options are incorrect
Option (2) \( Mg(s) || Mg^{2+}(0.130M) | Ag^+ (0.001M) || Ag(s) \) — Incorrect. The single and double lines are interchanged, so the salt bridge would sit between a metal and its own ions, and the \( \ce{Ag+} \) concentration is wrong.
Option (3) \( Mg(s) | Mg^{2+}(0.130M) || Ag(s) | Ag^+ (0.0001M) \) — Incorrect. The cathode is written in reverse; on the right-hand side the ion comes first and the metal last.
Option (4) \( Mg^{2+}(0.130M) | Mg(s) || Ag(s) | Ag^+ (0.0001M) \) — Incorrect. Both electrodes are written in reverse; the representation must start with the anode metal and end with the cathode metal.
NCERT (2026-27 edition):
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.”