Which of the following oxide groups cannot be reduced by carbon?

Electrolytic reduction of alumina to aluminium by the Hall-Heroult process is carried out in the presence of:

In the process of extraction of gold,
Roasted gold ore $+ CN^{-} + H_2O \xrightarrow{O_2} [x] + OH^{-}$;
$[x] + Zn \rightarrow [y] + Au$
$[x]$ and $[y]$ are :

The role of fluorspar $(CaF_2)$, which is added in small quantities in the electrolytic reduction of alumina $(Al_2O_3)$ dissolved in fused cryolite $(Na_3AlF_6)$, is:

Which of the following statements is not correct?
$1$. Reduction of alumina to give aluminium by magnesium is thermodynamically feasible.
$2$. The point of intersection of $Al_2O_3$ and $MgO$ curves in Ellingham diagram is below $1665 \ K$.
$3$. Use of magnesium as reducing agent in metallurgy of aluminium is economical.
$4$. Ellingham diagram represents the graphical plot of Gibbs energy vs temperature for the formation of the oxides of common metals and reducing agents.

Which of the following processes involves smelting?