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

Leaching of gold with dilute aqueous solution of $NaCN$ in presence of oxygen gives complex $[A]$,which on reaction with zinc forms the elemental gold and another complex $[B]$. $[A]$ and $[B],$ respectively are ...... .

The final step for the extraction of copper from copper pyrite in the Bessemer converter involves the reaction:

To obtain silver from silver amalgam,it is heated in a vessel which is made of

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.

Roasted copper pyrite on smelting with sand produces