Which one of the following is not a method of concentration of ore?

Observe the following statements regarding the purification of bauxite and select the correct answer.
$I$ : During the Hall's process,silicon is removed in the form of vapor.
$II$ : Bauxite containing $Fe_2O_3$ impurities is purified by the Bayer's process.
$III$ : During the Serpek's process,$AlN$ is formed.

Froth floatation process is used for the concentration of

Identify the product formed when bauxite ore is treated with sodium hydroxide?

Which of the following ores is concentrated by the leaching process?

In the extraction of $Al$,the chemical used in the Serpek process is: