Zone refining is based on the principle that

Options

A. impurities of low boiling metal can be seperated by distillation.
B. impurities are more soluble in molten metal than in solid metal.
C. different components of a mixture are differently adsobed on an adsorbent
D. vapours of volatile compound can be decomposed to pure metal.

Explanation

**Step-by-Step Solution:**

1. **Understanding Zone Refining**: Zone refining is a purification process used primarily for metals, particularly semiconductors like germanium and silicon. It is employed after the extraction of metals from their ores to remove impurities.

2. **Principle of Zone Refining**: The fundamental principle of zone refining is that impurities are more soluble in the molten state of the metal than in its solid state. This means that when the metal is melted, the impurities tend to dissolve in the liquid metal.

3. **Process Description**:
- A circular mobile heater is placed at one end of the impure metal rod.
- As the heater moves along the rod, it melts the metal in its vicinity, creating a molten zone.
- The impurities, which are more soluble in the molten metal, move along with the molten zone as the heater progresses.
- When the molten metal solidifies behind the heater, it crystallizes, leaving the impurities in the molten zone.

4. **Repetition of the Process**: This process is repeated multiple times. Each time the heater moves, more pure metal crystallizes out while the impurities are pushed further along the rod.

5. **Final Outcome**: Eventually, after several passes, the impurities concentrate at one end of the rod, which can then be cut off to obtain the purified metal.

6. **Conclusion**: Therefore, the correct answer to the question is that zone refining is based on the principle that "impurities are more soluble in the molten metal than in the solid metal."

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