You are an alchemist who is trying to remove hard lead impurity from Crude silver. You can only use thermal refining by using a blast of air. What would you use?
Options a and b are both part of vapour phase refining while option d is applicable for steel making. Cupellation is carried out on a boat shaped container in which the surface of the molten impure metal is treated with a blast of hot air. The impurities are oxidized to volatile oxides and they escape with the blast.