Coke powder is spreaded over the molten electrolyte in electrolytic reduction of ${\mathrm{A}1}_2{\mathrm{O}}_3$ in order to:

In the electrolytic reduction of ${\mathrm{A}1}_2{\mathrm{O}}_3$, coke powder is applied over the molten electrolyte to block heat radiation from the surface and avoid corrosion of the graphite anode.

Coca-Cola stops the airborne burning of graphite electrodes (oxygen). Therefore, we may conclude that powdered coke reduces the radiation-induced loss of heat and the corrosion of the graphite anode.

Hence Correct option is D