The concentration of chromite ore $(FeO \cdot Cr_2O_3)$ is done by which of the following methods?

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:

Froth floatation process is used for the concentration of the ore of

$4 Ag_{(s)} + 8 CN^{-}_{(aq)} + 2 H_2O_{(l)} + O_{2(g)} \longrightarrow 4 [Ag(CN)_2]^{-}_{(aq)} + 4 OH^{-}_{(aq)}$
The above reaction represents the process of concentration of ore in the extraction of silver. This process is:

What is the significance of leaching in the extraction of aluminium?

Chemical leaching is useful in the concentration of