Boron and silicon of very high purity can be obtained through :

Solution

Chemistry ma’am · 3 steps

Semiconductor-grade purity means zone refining: impurities prefer the melt and get swept to one end.

1. The principle. Impurities are more soluble in the molten element than in the solid. So when a melt freezes, the crystal that forms is purer than the liquid it came from.
2. How it works. A ring heater moves slowly along a rod of impure element, melting a narrow zone. Pure solid crystallises behind the heater, and the impurities travel forward with the molten zone. Repeating the pass several times collects them at one end, which is then cut off.

   Method	Used for
   Liquation	low-melting metals such as Sn
   Electrolytic refining	metals such as Cu and Zn
   Zone refining	ultra-pure Si, Ge, B, Ga, In
   Vapour phase refining	Ni (Mond process), Zr and Ti (van Arkel process)

3. So. Boron and silicon of very high purity, as needed for semiconductors, are obtained by zone refining, option (c).

The idea to keep. Whenever a question says very high purity or semiconductor grade (Si, Ge, B, Ga, In), think zone refining. It works because impurities stay in the melt.

Answer from the NTA final answer key. Solution by PrepWiser.