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Germanium and silicon used as semiconductors are purified by zone refining because
Atheir oxides are highly volatile on strong heating
Bthey readily form volatile iodides with iodine
Cthey possess unusually low melting points
Dimpurities stay more soluble in the molten zone
Answer & Solution
Correct answer: D. impurities stay more soluble in the molten zone
1. Zone refining relies on fractional crystallisation: when the metal re-solidifies, **impurities prefer to stay in the molten (liquid) zone**.
2. A mobile heater is moved along the rod so the molten zone (carrying impurities) sweeps to one end.
3. Repeating this leaves ultra-pure metal, ideal for semiconductors like Ge, Si and Ga.
_Source: Samacheer Kalvi Class 12 Chemistry Vol.1, Unit 1 'Metallurgy', §1.6.4 (Zone refining)_
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