Gallium and Indium can be prepared by:

The correct answer is Option (1) → Zone refining

Zone refining gives metals of very high purity, such as germanium, silicon, boron, gallium and indium; it works because the impurities are more soluble in the melt than in the solid metal.

Why the other options are incorrect

• Option (2) Vapour phase refining — Incorrect. The metal is converted into a volatile compound that is then decomposed; it is used for nickel (Mond process) and zirconium/titanium (van Arkel method), not for Ga and In.

• Option (3) Mond process — Incorrect. It is specific to nickel, which forms volatile \( \ce{Ni(CO)4} \).

• Option (4) van Arkel method — Incorrect. It purifies Zr and Ti through their volatile iodides decomposed on a hot filament.

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 – “This method is based on the principle that the impurities are more soluble in the melt than in the solid state of the metal. A circular mobile heater is fixed at one end of a rod of the impure metal. The molten zone moves along with the heater which is moved forward. As the heater moves forward, the pure metal crystallises out of the melt and the impurities pass on into the adjacent molten zone. The process is repeated several times and the heater is moved in the same direction. At one end, impurities get concentrated. This end is cut off. This method is very useful for producing semiconductor and other metals of very high purity, e.g., germanium, silicon, boron, gallium and indium.”