Which method is used for the concentration of the ore containing iron chromate $(FeCrO_4)$?

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.

What is the significance of leaching in the extraction of aluminium?

How is leaching carried out in case of low grade copper ores?

$A$ substance which reacts with gangue to form fusible material is called:

Cassiterite is concentrated by