The correct options are
A ultra pure boron
C ultra pure silicon
Zone refining is based upon fractional crystallization as the impurity prefers to stay in the melt and on solidification only pure metals solidifies on the surface of melt.
In this process solubility of the impurities in the metal in molten and solid states is different.
Metals like Si, Ge, Ga and B of high purity are purified by this method.
This process is known as ultra-purification because it results in impurity level decreasing to ppm level.