Electrochemistry
A galvanic cell is an electrochemical cell that converts the chemical energy of a spontaneous redox reaction into electrical energy whereas, an electrolytic cell is a device which uses electrical energy to carry out the non-spontaneous chemical reactions. We can construct innumerable number of galvanic cells on the pattern of Daniell cell (Cu-Zn cell) by taking combinations of different half-cells. Each half-cell consists of a metallic electrode dipped into an electrolyte. The two half-cells are connected by a metallic wire through a voltmeter and a switch externally. The electrolytes of the two half-cells are connected internally through a salt bridge. In a galvanic cell, the half-cell in which oxidation takes place is called anode and it has a negative potential with respect to the solution and in an accepted convention we keep the anode on the left and the cathode on the right side. 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.
If the nickel electrode dipped in aqueous solution of nickel chloride is anode and silver electrode dipped in aqueous solution of silver nitrate is cathode. The galvanic cell is represented by:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Ni(s)|Ni2+(aq.)||Ag+(aq.)|Ag(s)
A galvanic cell is written by these conventions:
The anode (oxidation) is written on the left and the cathode (reduction) on the right.
A single vertical line (|) separates the metal from its solution; a double vertical line (||) stands for the salt bridge.
Each ion is written with its real charge; the coefficients of the balanced equation are not written.
Here nickel is the anode and silver is the cathode:
\( \displaystyle \text{Anode: }\ce{Ni(s) -> Ni^2+(aq) + 2e^-} \)
\( \displaystyle \text{Cathode: }\ce{Ag^+(aq) + e^- -> Ag(s)} \)
So the cell is represented as Ni(s) | Ni2+(aq) || Ag+(aq) | Ag(s).
Why the other options are incorrect
Option (1) Ni(s)|Ni2+(aq.)||Ag2+(aq.)|2Ag(s) — Incorrect. Silver nitrate gives Ag+, not \( \ce{Ag^{2+}} \), and coefficients such as “2Ag” are not written in cell notation.
Option (2) Ag(s)|Ag2+(aq.)||Ni2+(aq.)|Ni(s) — Incorrect. This puts the cathode (silver) on the left; it also uses \( \ce{Ag^{2+}} \).
Option (3) Ni2+|Ni(s)||Ag(s)|Ag(aq.) — Incorrect. The order inside each half-cell is wrong (the anode half-cell is written metal | ion), and “Ag(aq.)” is not an ion.
NCERT (2026-27 edition):
Galvanic Cells – …
