Question

The method of zone refining of metals is based on the principle of:
(A) greater mobility of the pure metal than that of impurity
(B) higher melting point of the impurity then that of the pure metal
(C) greater noble character of the solid metal than that of the impurity
(D) greater solubility of the impurity in the molten state than in the solid state

Answer 1

The general information about the method of zone refining can help us answer the above question. The principle will be the first and prior most thing to be considered while explaining this method.

Complete answer:
Let us study about the method of zone refining in detail.
Zone refining-
This method is also referred to as zone melting, travelling melting zone and floating zone process. It is a very useful method to get metals with very high purity such as silicon, gallium and germanium.
This method refers to the process of purifying a crystal while a thin region of crystal undergoes melting. The impurities present in the metal are melted by the moving molten zone at the forward edge and the solidified pure element is thus left behind.
Process-
In this process, a circular mobile heater is fixed at one end of the metal rod which is basically impure metal or an ore. Then the heater is moved across the length of the metal rod.
The pure metal is left solidified at the positions of the rod and the impurities are melted and those are moved along with the heater. This is because the impurities are readily soluble in the mobile heater as compared to the pure metal.
Thus, the solidified metal is at one end of the rod and the impurities are moved at the other end of the rod by the mobile heater which can then be easily removed. In this way, the metal is purified.
By this, we can say that the process is based on the principle that the impurities in the ore are more soluble in the melt state than that of the corresponding solid state.

Therefore, option (D) is correct.

Note:
Do note that in the method of zone refining, the molten zone contains more impurity than that of the original and pure metal.