The method used for the purification of Indium is:

Indium is a semiconductor-grade metal that requires very high purity. The method used for its purification is zone refining.

Zone refining is based on the principle that impurities are more soluble in the molten state (melt) than in the solid state. A narrow zone of the metal is melted using a circular heater, and this molten zone is slowly moved along the length of the rod. As the molten zone advances, impurities preferentially remain in the melt and are swept to one end of the rod. The process is repeated several times to achieve ultra-high purity.

This method is particularly suited for elements like indium, germanium, silicon, and gallium that are used in semiconductor applications where extremely high purity (99.9999%) is required.

Therefore, the correct answer is option (3): zone refining.