Which refining method is represented by the following equations?
\(Zr + 2I_2 \longrightarrow ZrI_4\)
\(ZrI_4 \longrightarrow Zr + 2I_2\)
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → van Arkel method
In vapour phase refining the crude metal is turned into a volatile compound, which is collected and then decomposed to give the pure metal. In the van Arkel method the volatile compound is the metal iodide:
\( \ce{Zr + 2I2} \xrightarrow{\text{heat, evacuated vessel}} \ce{ZrI4} \) (volatile iodide formed)
\( \ce{ZrI4} \xrightarrow{\text{W filament, about 1800 K}} \ce{Zr + 2I2} \) (iodide decomposed, pure Zr deposited)
Why the other options are incorrect
Option (1) Zone refining — Incorrect. A molten zone is moved along a rod of the metal and the impurities collect in the melt; no iodide is formed. It is used for Si, Ge, B and Ga.
Option (2) Mond process — Incorrect. It is also vapour phase refining, but nickel is refined through its volatile carbonyl, \( \ce{Ni(CO)4} \), formed with CO; no iodine is used.
Option (4) Electrolytic method — Incorrect. The impure metal is made the anode in an electrolytic cell and the pure metal collects on the cathode; the equations given involve no electrolysis.
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):
Vapour Phase Refining – …
