Which of the following ores is concentrated by the process of leaching?

In the leaching method,bauxite ore is digested with a concentrated solution of $NaOH$ that produces $X$. When $CO_2$ gas is passed through the aqueous solution of $X$,a hydrated compound $Y$ is precipitated. $X$ and $Y$ respectively are

In the purification of bauxite by Hall's process:

The correct statements regarding the froth floatation method in metallurgy are:
$I$. Used for the purification of sulphide ores
$II$. Used for the roasting of sulphide ores
$III$. It is based on the relative densities of gangue and ore particles
$IV$. It is based on the difference in the wetting properties of gangue and ore particles in frothing agent and water

Froth flotation process is used for the concentration of:

In metallurgy,the term "gangue" is used for: