Gallium and Indium can be prepared by:

Zone refining

The correct answer is option 1. Zone refining.

Zone refining is a technique used to purify metals and semiconductors by exploiting the fact that impurities tend to concentrate in the molten phase of a material. Here’s a step-by-step explanation of how it works:

Starting Material: You start with a piece of metal that contains impurities.

Heating and Melting: A small region of the metal is heated to melt it. This molten zone is moved along the length of the metal rod or bar.

Impurity Movement: As the molten zone moves, impurities within the metal tend to move with it. The reason for this is that impurities are generally more soluble in the molten phase than in the solid phase.

Solidification: When the molten zone solidifies, the impurities are concentrated in the liquid part of the metal that is left behind, which eventually solidifies as well. This means that as you move the molten zone along, the impurities are pushed ahead and concentrated in a particular region.

Repeated Process: This process can be repeated several times to achieve high purity. Each pass through the molten zone removes a little more of the impurities, concentrating them in a specific section.

Final Purification: After several passes, the impurities are found in the end portion of the rod, which can then be removed or discarded, leaving behind the purified metal.

Advantages of Zone Refining:

High Purity: It can achieve extremely high levels of purity, which is crucial for semiconductors and other applications.

Selective Removal: The technique is particularly effective for removing specific types of impurities.

Applications:

Semiconductors: Used to purify materials like silicon, gallium, and indium for electronic devices.

Specialty Metals: Useful for metals used in high-precision applications where impurities can drastically affect performance.

This method is particularly suited for metals like gallium and indium because it allows for the effective separation of these metals from their impurities, achieving the required high purity for advanced technological applications.