Which of the following methods is $NOT$ used for the purification of metals?

In the zone-refining method,the molten zone:

Poling is employed in the refining of:

In the electrolytic refining of metals,the electrolysis of an aqueous solution of its complex salt is performed using an impure metal as the anode and a strip of pure metal as the cathode. This method cannot be used for the refining of which of the following metals?

Which of the following processes for refining of metals involves a principle of selective adsorption of the components from a mixture?

Give two requirements for vapour phase refining.