Zone refining is based on the principle that

Options

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

Answer

**Step-by-Step Solution:**

1. **Understanding Zone Refining:**
Zone refining is a technique used to purify metals. It is particularly effective for removing impurities from a solid metal.

2. **Principle of Solubility:**
The core principle behind zone refining is based on the solubility of impurities. In this process, it is observed that impurities have a higher solubility in the molten state of the metal compared to its solid state.

3. **Heating the Metal:**
During zone refining, a metal rod is heated in a localized area using a heater. This creates a molten zone where the temperature is significantly higher than the surrounding solid metal.

4. **Movement of Impurities:**
As the heater moves along the rod, the molten zone also moves. Impurities that are present in the solid metal tend to dissolve in the molten metal more readily.

5. **Separation of Pure Metal:**
After the heater has moved along the length of the rod, the molten region solidifies again. The impurities that have dissolved in the molten metal are then moved along with the molten zone. The portion of the rod that contains the impurities can be cut off, leaving behind a purer section of the metal.

6. **Conclusion:**
Therefore, the principle of zone refining can be summarized as: "Impurities are more soluble in molten metal than in solid metal." This principle allows for effective purification of metals.

**Final Answer:**
Zone refining is based on the principle that impurities are more soluble in molten metal than in solid metal.

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