When the cell reaction in a voltaic cell is reversed by reversing the…

The correct answer is Option (2) → an electrolytic cell

• A voltaic (galvanic) cell uses a spontaneous reaction to produce electricity; an electrolytic cell uses electricity from outside to drive a non-spontaneous reaction. In the Daniell cell (1.1 V), an opposing external voltage above 1.1 V reverses the electron flow, and with it the cell reaction:

      \( \displaystyle \ce{Zn^2+(aq) + Cu(s) -> Zn(s) + Cu^2+(aq)} \)

• Zinc is now deposited and copper dissolves. Electrical energy is being used to carry out a non-spontaneous reaction, so the device works as an electrolytic cell.

Why the other options are incorrect

Option (1) a reversible cell — Incorrect.

• “Reversible” describes a cell whose reaction can be driven back by an opposing voltage, as the Daniell cell is.

• It is not a new kind of cell; while the reaction runs backwards, the device is working as an electrolytic cell.

Option (3) a concentration cell — Incorrect. A concentration cell has the same electrode in solutions of different concentration. Reversing the electron flow does not change the electrodes or the solutions.

Option (4) a fuel cell — Incorrect. A fuel cell is a galvanic cell that converts the energy of combustion of fuels such as hydrogen directly into electrical energy. It produces electricity; it does not use it.

NCERT (2026-27 edition):
2.1 Electrochemical Cells – “If an external opposite potential is applied in the galvanic cell [Fig. 2.2(a)] and increased slowly, we find that the reaction continues to take place till the opposing voltage reaches the value 1.1 V [Fig. 2.2(b)] when, the reaction stops altogether and no current flows through the cell. Any further increase in the external potential again starts the reaction but in the opposite direction [Fig. 2.2(c)]. It now functions as an electrolytic cell, a device for using electrical energy to carry non-spontaneous chemical reactions.”