The substance used as froth stabilisers in the froth-floatation process is

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.

The purification of alumina is called

What is the role of a depressant in the froth flotation process?

How do we separate two sulphide ores by the Froth Flotation Method? Explain with an example.

For the purification of alumina,the modern processes most useful when $(i)$ the impurity present is a lot of iron oxides and $(ii)$ the impurity present is a lot of silica,are: