Reagent used in Bayer's process of concentration of bauxite ore is:

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

Select the correct option regarding the method of separating two sulfide ores by the froth flotation process.
$(1)$ The ratio of water and oil is chosen appropriately.
$(2)$ Some depressants are used for this process.
$(3)$ $HCN$ is a depressant for a mixture of $ZnS$ and $PbS$.
$(4)$ By using a suitable depressant for a mixture of $ZnS$ and $PbS$,only $PbS$ comes up with the froth.

The purification of alumina is called

Ores like magnetite or tungstates in tin ores are concentrated by

The beneficiation of the sulphide ores is usually done by