Question

A galvanic cell functions like an electrolytic cell when :

• A. \( E_{\mathrm{cell}} = E_{\mathrm{ext}} \)
• B. \( E_{\mathrm{cell}} > E_{\mathrm{ext}} \)
• C. \( E_{\mathrm{ext}} > E_{\mathrm{cell}} \)
• D. \( E_{\mathrm{cell}} = 0 \)

Hint:

When the opposing external potential exceeds the cell potential, the reaction reverses and the cell is electrolytic.

Answer 1

The Correct Option is C

Step 1: Recall the Daniell cell set-up.
In a galvanic cell the cell reaction pushes electrons from anode to cathode.
An external opposing potential \( E_{\mathrm{ext}} \) can be applied in the opposite direction, and the cell behaves differently depending on its size.

Step 2: Check option (A).
If \( E_{\mathrm{ext}} = E_{\mathrm{cell}} \), the two cancel. No current flows and the reaction stops. The cell is neither galvanic nor electrolytic. So (A) is wrong.

Step 3: Check option (B).
If \( E_{\mathrm{cell}} > E_{\mathrm{ext}} \), the cell still drives current in its own direction. It works as a galvanic cell. So (B) is wrong.

Step 4: Check option (C).
If \( E_{\mathrm{ext}} > E_{\mathrm{cell}} \), the outside source wins. Current flows in the reverse direction and the cell reaction is reversed.
Electrical energy now drives a non-spontaneous reaction, which is electrolysis. So (C) is correct.

Step 5: Check option (D).
\( E_{\mathrm{cell}} = 0 \) means the cell is at equilibrium or dead. It cannot work as an electrolytic cell by itself. So (D) is wrong.

Final Answer:
A galvanic cell acts as an electrolytic cell when the external potential is larger than the cell potential. \[ \boxed{E_{\mathrm{ext}} > E_{\mathrm{cell}}} \]