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

Which of the following ores can be concentrated by the froth flotation method?

Leaching is commercially carried out for the concentration of which of the following ores?

$NaCN$ is sometimes added in the froth flotation process as a depressant when $ZnS$ and $PbS$ minerals are expected because

When $ZnS$ and $PbS$ minerals are present together,then $NaCN$ is added to separate them in the froth floatation process as a depressant,because

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: