Thermite is a mixture of

Statement $I :$ Leaching of gold with cyanide ion in absence of air $/$ $O_2$ leads to cyano complex of $Au(III)$.
Statement $II :$ Zinc is oxidized during the displacement reaction carried out for gold extraction.
In the light of the above statements,choose the correct answer from the options given below.

Carbon cannot be used in the reduction of $Al_2O_3$ because

The slag consists of molten impurities generally in the form of

The electrolytic method of reduction is employed for the preparation of metals that

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.