The correct option is C cathode to anode through internal supply
In electrolytic cell, electrolysis occur at the cost of electricity.
In electrolytic cell, the cathode is the electrode connected to the negative terminal and the anode is connected to the positive terminal.
Therefore the cathode acts as source of electrons and hence inside an electrolytic cell the electrons move from the cathode to anode internally.
Mn+ + ne → M (Electron gone in solution)
Xn− → X + ne (Electron supplied to anode)
Therefore, electron is moving from cathode to anode via internal circuit.