A variable, opposite external potential (Eext) is applied to the cell Zn|Zn2+(1M)||Cu2+(1M)|Cu, of potential 1.1 V. When Eext < 1.1 V and Eext > 1.1 V respectively electron flow from:

When Eext < 1.1 V, the electrons will flow from anode to cathode, the cell will act as the galvanic cell. When Eext > 1.1 V, electrons will flow from cathode to anode and the cell will act as an electrolytic cell. Hence, option B is correct.