Solution:
Concept- (i) Zone refining is used to refine impurities such as Si, B, Ga, In, and other metals that are more soluble in molten states than in solid states. This process is used to purify semiconductors such as Si, Ge, and Ga. In liquid metal, impurities are far more soluble than in solid metal. Fractional crystallisation is used in this procedure. A rod of impure metal is surrounded by a circular heater. When the heater is moved, the pure metal crystallises and the impurities pass into the molten metal next to it. The impurities are shifted to one end of the metal, which is then cut off.(ii) Electrorefining is a process for purifying impure zinc. The cathode is pure zinc, while the anode is impure zinc. The anode in this process is impure copper metal, while the cathode is pure copper metal. The electrolyte is a water-based solution of copper salt. Impure metal from the anode releases metal ions into the solution, and metal ions from the solution generate metal at the cathode. In the case of copper, the waste under the anode (anode mud) may contain precious metals like gold, silver, zinc, and so on.
(iii) Vapour phase refining: Metal is transformed into a volatile chemical, which is then degraded to get pure metal. It is the process of turning a metal into a volatile chemical and then decomposing it to produce a pure metal. With a readily available reagent, the metal should create a volatile chemical. Nickel, zirconium, and titanium are examples of volatile compounds that are easily dissolved such that the metal can be retrieved.
Hence, the answer is option 2.
