Answer:
(b) Zone
refining is based on the principle that the impurities are more soluble in
molten state than in solid state of the metal. A circular mobile heater fixed
at one end of impure metal rod. The molten zone moves along with heater which
is moved forward.
As the heater moves
forward, the pure metal crystallises out of the melt and the impurities pass on
into adjacent molten zone. The process is repeated several times and the heater
is moved in the same direction.
At one end,
impurities get concentrated. This end is cut off. e.g., germanium, silicon, gallium
etc., are refined by this method.
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