A galvanic cell can be converted to an electrolytic cell when
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Eext > 1.1 V
The Daniell cell has E = 1.1 V:
\( \ce{Zn(s) + Cu^2+(aq) -> Zn^2+(aq) + Cu(s)} \)
When an external opposite potential greater than 1.1 V is applied, the reaction runs in the opposite direction: electrons flow from Cu to Zn, zinc is deposited and copper dissolves. The cell now uses electrical energy to drive a non-spontaneous reaction, so it is an electrolytic cell:
\( \ce{Zn^2+(aq) + Cu(s) -> Zn(s) + Cu^2+(aq)} \)
Why the other options are incorrect
Option (1) Eext < 1.1 V — Incorrect. The cell keeps working in its normal (galvanic) direction.
Option (2) Eext = 1.1 V — Incorrect. The two potentials balance; there is no reaction in either direction.
Option (4) the chemical reaction stops on completion — Incorrect. A cell that has run down is exhausted; it does not become an electrolytic cell.
NCERT (2026-27 edition):
Electrochemical Cells – …
