Which one of the following is true?

How can you separate alumina from silica in bauxite ore associated with silica? Give equations,if any.

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

Which of the following statements is not correct?
$(i)$ Froth-floatation is used for removing gangue from sulphide ore.
$(ii)$ Cresols are used to stabilise the froth.
$(iii)$ Sodium cyanide can be used as depressant for preferential separation.
$(iv)$ Aniline can be used as froth enhancer.

The process which involves the treatment of the ore with a suitable reagent so as to make it soluble but not the impurities is called:

The function of potassium ethyl xanthate in the froth floatation process is to make the ore