Given below are the steps involved in the process of zone refining for removing impurities which are more soluble in the melt than solid state of the metal.
- Impurities get concentrated at one end
- As the heater moves forward, the pure metal crystallizes out of the melt left behind and the impurities pass to the next zone
- A mobile heater surrounding the rod of impure metal is fixed at its one end.
- The end is cut off.
- The molten zone moves along with the heater which is moved forward.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → C, E, B, A, D
Zone refining works on the principle that impurities are more soluble in the melt than in the solid metal. A narrow molten zone is passed along a rod of impure metal; the pure metal crystallises behind the zone while the impurities travel with it. The steps follow one another:
C. A mobile heater surrounding the rod of impure metal is fixed at its one end — this creates a molten zone at that end.
E. The molten zone moves along with the heater which is moved forward.
B. As the heater moves forward, the pure metal crystallises out of the melt left behind and the impurities pass to the next zone.
A. After repeated passes, the impurities get concentrated at one end.
D. The end containing the impurities is cut off.
Shortcut: Options (3) and (4) both start with C and end with D; the molten zone must move (E) before the pure metal can crystallise behind it (B), which gives Option (3).
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
