Which zone of the blast furnace has the highest temperature?

Which statement is incorrect regarding the Hall-Heroult process for the metallurgy of aluminium?
$1$. Use of $Na_3AlF_6$ lowers the melting point of $Al_2O_3$.
$2$. Steel vessel with a lining of carbon acts as the cathode.
$3$. Graphite is used as the anode.
$4$. Carbon dioxide gas is generated at the cathode.

Copper is extracted from sulphide ore using the method:

Which statement is correct?

Extraction of gold and silver involves leaching with $CN^{-}$ ion. Silver is later recovered by

Which of the following reactions takes place during the smelting process?