Which flux is used to remove $SiO_2$ impurity?

Limestone is used as a flux in the extraction of

In the extraction of iron from haematite,the impurity $(x)$ of the ore is removed in the form of '$y$'. What are $x$ and $y$ respectively?

In the metallurgy of aluminium,cryolite is mixed in the molten state because it

Impure silver ore $+ CN^{-} + H_2O \xrightarrow{O_2} [X]^{-} + OH^{-}$
$[X]^{-} + Zn \longrightarrow [Y]^{2-} + Ag \text{ (pure)}$
The coordination numbers of the metals in $[X]$ and $[Y]$ are respectively

For which of the following metals is the self-reduction process $NOT$ used?