How is magnesium obtained from the following?

Given are two statements,one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$: Magnesium can reduce $Al_{2}O_{3}$ at a temperature below $1350^{\circ} C$,while above $1350^{\circ} C$ aluminium can reduce $MgO$.
Reason $R$: The melting and boiling points of magnesium are lower than those of aluminium.
In light of the above statements,choose the most appropriate answer from the options given below:

The chemical that is added to reduce the melting point of the reaction mixture during the extraction of aluminium is

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 :

Which one of the following oxides is reduced by water gas to obtain the metal during its extraction?

Which of the following is $NOT$ a process used for the extraction of silver?