The correct option is A impure
Electrorefining of Metals: Metals such as Cu,Ag,Zn,Sn,Pb,Al,Ni,Cr are purified by this method. The impure metal is used as the anode of an electrolytic cell, while the cathode is a thin plate of pure metal. The electrolyte is the solution of a double salt of the metal. On passing electric current, pure metal from the anode dissolves and gets deposited at the cathode. The soluble impurities go into the solution while insoluble or less electropositive impurities settle down below the anode as anode mud or sludge.