In metallurgy,the term "gangue" is used for:

When $ZnS$ and $PbS$ minerals are present together,then $NaCN$ is added to separate them in the froth floatation process as a depressant,because

In the Serpek process for the purification of bauxite,what is used to remove silicon dioxide?

In the extraction of $Al$,the chemical used in Serpeck's process is:

Which of the following ores is concentrated by the froth flotation process?

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.