Which one of the following is not a method of concentration of metals?

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.

In the leaching of alumina from bauxite,the ore impurity expected to leach out in the process by reacting with $NaOH$ is:

Name the reagent that is used in leaching of gold.

Which soluble substances are obtained when bauxite is treated with a solution of $NaOH$ at a temperature of $473 - 523 \ K$ and a pressure of $35 - 36 \ bar$?

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