Froth flotation method is used for the concentration of which type of ores?

In the concentration of $PbS$ containing $ZnS$ as impurity,the depressant used is:

Explain the concentration of ore by Hydraulic Washing.

During initial treatment,preferential wetting of ore by oil and gangue by water takes place in

Magnetic separation is used for increasing the concentration of which of the following ores?

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.