Ultra pure silicon can be obtained by
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Zone refining
Zone refining works because the impurities are more soluble in the melt than in the solid metal. Repeated passes of the molten zone carry the impurities to one end, which is cut off. This gives the very high purity needed for semiconductors such as silicon.
Why the other options are incorrect
Option (1) Distillation — Incorrect. Used for low boiling metals such as zinc and mercury; silicon is not purified this way.
Option (2) Electrolytic refining — Incorrect. Used for metals such as copper and zinc; it does not give the ultra-high purity needed for semiconductors.
Option (3) Vapour phase refining — Incorrect. The metal is turned into a volatile compound and decomposed again, as in the Mond process for nickel and the van Arkel method for zirconium and titanium; it is not the method for ultra pure silicon.
Note: This question is from the pre-rationalised NCERT book (2022-23). The topic is not there in the latest NCERT book (2026-27), and it is also out of the CUET 2026 syllabus.
NCERT (Pre-rationalised edition, 2022-23):
Zone Refining
