The correct option is A NaCl+KCl+KF
The Downs cell uses a carbon anode and an iron cathode. The preferred electrolyte is fused sodium chloride. Though solid sodium chloride
is a poor conductor of electricity, in the fused state the sodium and chloride ions are mobilized and thus become charge carriers.
Some KCl and even KF are added to the electrolyte to lower the temperature required to keep the electrolyte liquid.
Sodium chloride melts at 801 ° C, but a salt mixture could be fused at a temperature as low as 507 °C.
The anode reaction is:
2Cl−⟶Cl2(g)+2e−
The cathode reaction is:
2Na++2e−⟶2Na(l)
Overall reaction:
2Na++2Cl−⟶2Na(l)+Cl2(g)