The Galvanic cells will behave like an electrolytic cell when
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → \(E_{cell} < E_{ext}\)
A galvanic cell converts the energy of a spontaneous redox reaction into electrical energy. If an external potential opposing the cell is applied and slowly increased, three situations arise. For the Daniell cell (\( E_{cell} = 1.1\ \mathrm{V} \)):
\( E_{ext} \lt E_{cell} \): the cell reaction continues; electrons flow from Zn to Cu, zinc dissolves and copper is deposited.
\( E_{ext} = E_{cell} \): the reaction stops and no current flows.
\( E_{ext} \gt E_{cell} \): the reaction is reversed; electrons flow from Cu to Zn, zinc is deposited and copper dissolves.
In the last case electrical energy from outside drives a non-spontaneous reaction, which is what an electrolytic cell does:
\( \displaystyle \ce{Zn^2+ + Cu -> Zn + Cu^2+} \quad (E_{ext} \gt 1.1\ \mathrm{V}) \)
So the galvanic cell behaves as an electrolytic cell when \( E_{cell} \lt E_{ext} \).
Why the other options are incorrect
Option (1) \(E_{cell} =0\) — Incorrect. A cell with zero potential is at equilibrium (a dead cell); it neither gives nor uses current.
Option (2) \(E_{cell} > E_{ext}\) — Incorrect. The cell is still stronger than the opposing potential, so it keeps working as a galvanic cell.
Option (4) \(E_{cell} = E_{ext}\) — Incorrect. The two potentials balance; no current flows and no reaction takes place.
NCERT (2026-27 edition):
Electrochemical Cells – …
