The correct cell representation from the following is:
A. \(Pt (s) | H^+ (aq) | H_2 (g) (\text{1 atm}) ||Ag^+ (aq) | Ag (s)\)
B. \(Pt (s) | Br_2 (l) | Br^- (aq) || Au^{3+} (aq) | Au (s)\)
C. \(Al (s) | Al^{3+} (aq) || H_2 (g) (\text{1 atm}) | H^+ (aq) | Pt (s)\)
D. \(Cu (s) | Cu^{2+} (aq) || Cl^- (aq) | Cl_2 (g) (\text{1 atm}) | Pt (s)\)
E. \(Pt (s) | Cl^- (aq) | Cl_2 (g) (\text{1 atm}) ||Co^{3+} (aq) | Co^{2+} (aq) | Pt (s)\)
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → B and D only
A galvanic cell is written with the anode on the left and the cathode on the right. A single vertical line separates two phases (for example a metal and its solution, or a gas and a solution), a double line stands for the salt bridge, and two ions present in the same solution are separated by a comma, not by a line. A gas electrode needs an inert Pt electrode at the outer end; the hydrogen electrode is written Pt(s)|H2(g)|H+(aq) as the anode and H+(aq)|H2(g)|Pt(s) as the cathode.
(A) Pt (s) | \( \ce{H^{+}} \) (aq) | \( \ce{H2} \) (g) (1 atm) ||\( \ce{Ag^{+}} \) (aq) | Ag (s) — Incorrect representation. The hydrogen anode is written Pt | \( \ce{H^{+}} \) | \( \ce{H2} \); it should be Pt(s) | H2(g) | H+(aq).
(B) Pt (s) | \( \ce{Br2} \) (l) | \( \ce{Br^{-}} \) (aq) || \( \ce{Au^{3+}} \) (aq) | Au (s) — Correct representation. Anode on the left with Pt at the outer end and a phase line between liquid \( \ce{Br2} \) and the \( \ce{Br^{-}} \) solution; cathode \( \ce{Au^{3+}} \) | Au on the right:
\( \displaystyle \text{Anode: }\ce{2Br^- -> Br2 + 2e^-} \)
\( \displaystyle \text{Cathode: }\ce{Au^3+ + 3e^- -> Au} \)
\( \displaystyle \text{Cell reaction: }\ce{6Br^- + 2Au^3+ -> 3Br2 + 2Au} \)
(C) Al (s) | \( \ce{Al^{3+}} \) (aq) || \( \ce{H2} \) (g) (1 atm) | \( \ce{H^{+}} \) (aq) | Pt (s) — Incorrect representation. The hydrogen cathode is written \( \ce{H2} \) | \( \ce{H^{+}} \) | Pt; it should be H+(aq) | H2(g) | Pt(s).
(D) Cu (s) | \( \ce{Cu^{2+}} \) (aq) || \( \ce{Cl^{-}} \) (aq) | \( \ce{Cl2} \) (g) (1 atm) | Pt (s) — Correct representation. Anode Cu | \( \ce{Cu^{2+}} \) on the left; the chlorine cathode is written like the hydrogen cathode, ion | gas | Pt:
\( \displaystyle \text{Anode: }\ce{Cu -> Cu^2+ + 2e^-} \)
\( \displaystyle \text{Cathode: }\ce{Cl2 + 2e^- -> 2Cl^-} \)
\( \displaystyle \text{Cell reaction: }\ce{Cu + Cl2 -> Cu^2+ + 2Cl^-} \)
(E) Pt (s) | \( \ce{Cl^{-}} \) (aq) | \( \ce{Cl2} \) (g) (1 atm) ||\( \ce{Co^{3+}} \) (aq) | \( \ce{Co^{2+}} \) (aq) | Pt (s) — Incorrect representation. \( \ce{Co^{3+}} \) and \( \ce{Co^{2+}} \) are in the same solution, so they must be separated by a comma, Co3+(aq), Co2+(aq) | Pt(s); a phase line between them is wrong.
NCERT (2026-27 edition):
Galvanic Cells – “… The potential difference between the two electrodes of a galvanic cell is called the cell potential and is measured in volts. The cell potential is the difference between the electrode potentials (reduction potentials) of the cathode and anode. It is called the cell electromotive force (emf) of the cell when no current is drawn through the cell. 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.”