Observe the following statements regarding purification of bauxite:

I. During Hall's process, silica is removed as Si (vapour)

II. Bauxite are contaminated with $Fe_2O_3$ is purified in Baeyer's process.

III. During Serpeck's process, AIN is formed.

(a) I,II and III are correct

(b) Only I and II are correct

(c) Only I and III are correct

(d) Only II and III are correct