An ore like zinc blende is concentrated by

Observe the following statements regarding the purification of bauxite:
$I$. During Hall's process,silica is removed as $Si$ (vapour).
$II$. Bauxite ore contaminated with $Fe_2O_3$ is purified in Baeyer's process.
$III$. During Serpeck's process,$AlN$ is formed.
The correct answer is:

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

What is leaching? Explain with an example.

During the extraction of sodium aluminate from bauxite,the compounds of ....... are insoluble and precipitate out.

$PbS$ can be separated from $ZnS$ by electrostatic separation. Which property is involved in this method?