Question: A galvanic cell can behave as an electrolytic cell when:

• (a) $E_{\text{cell}} = E_{\text{ext}}$
• (b) $E_{\text{cell}} > E_{\text{ext}}$
• (c) $E_{\text{cell}} = 0$
• (d) $E_{\text{ext}} > E_{\text{cell}}$

Step 1 (Governing Principle): [0.5 Mark]

A galvanic cell converts chemical energy into electrical energy. When an external opposing potential ($E_{\text{ext}}$) is applied to the galvanic cell, the direction of the current and the chemical reaction depends on the magnitude of $E_{\text{ext}}$ relative to the cell potential ($E_{\text{cell}}$).

Step 2 (Step-by-Step Logical Deduction): [0.25 Mark]

• If $E_{\text{ext}} < E_{\text{cell}}$, electrons flow from anode to cathode (Galvanic cell operation).
• If $E_{\text{ext}} = E_{\text{cell}}$, no current flows (Equilibrium).
• If $E_{\text{ext}} > E_{\text{cell}}$, the external potential overcomes the cell potential, forcing electrons to flow in the reverse direction (from cathode to anode). This reverses the chemical reaction, causing the cell to function as an electrolytic cell.

Step 3 (Final Concluded Answer): [0.25 Mark]

The correct option is (d) $E_{\text{ext}} > E_{\text{cell}}$.

💡 EL10 Concept Insight: Think of it like a hill: normally, a ball (electrons) rolls down naturally (Galvanic). If you push the ball harder from the bottom than it is rolling down, you force it to go back up the hill (Electrolytic).