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

The metal extracted by leaching with a cyanide is

Depressant used in the concentration of an ore containing $ZnS$ and $PbS$ is

Sulphide ores of metals are usually concentrated by froth floatation process. Which one of the following sulphide ores offers an exception and is concentrated by chemical leaching?

In the extraction of aluminium:
Process $X$: applied for red bauxite to remove iron oxide (chief impurity).
Process $Y$: (Serpeck's process) applied for white bauxite to remove $Z$ (chief impurity).
Then,process $X$ and impurity $Z$ are:

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