Zone refining is mainly used for:

Ga

Zone refining is a purification process that is used to produce high-purity metals. It is a relatively slow process, but it is very effective at removing impurities.

Zone refining works by melting a narrow zone of a metal and then moving the molten zone through the solid metal. The impurities in the metal tend to concentrate in the molten zone. As the molten zone moves through the solid metal, the impurities are left behind.

Zone refining is most commonly used to purify metals that have a high melting point and a low diffusion coefficient of impurities. This is because the zone refining process is most effective when the impurities are less likely to diffuse back into the solid metal from the molten zone.

The following metals are commonly purified using zone refining:

• Silicon
• Germanium
• Gallium
• Indium
• Arsenic
• Antimony
• Tellurium

Of the metals you have listed, only gallium is commonly purified using zone refining. Therefore, the answer is (2).

Nickel, zirconium, and tantalum are all high-melting-point metals, but they have high diffusion coefficients of impurities. This means that the impurities in these metals are more likely to diffuse back into the solid metal from the molten zone, making zone refining less effective.

Zone refining is a very important process for the production of high-purity metals. These metals are used in a variety of applications, including semiconductors, electronics, and aerospace.