Which of the following metals cannot be obtained by auto-reduction of their compounds?

In the extraction of silver,the following reactions take place:
$Ag_2S + NaCN \rightarrow A$
$A + Zn \rightarrow B$
If $B$ is a metal,identify $A$ and $B$.

Aluminium is extracted from alumina $(Al_2O_3)$ by electrolysis of a molten mixture of

Consider the following metallurgical processes:
$(i)$ Heating impure metal with $CO$ and distilling the resulting volatile carbonyl (boiling point $43\,^{\circ}C$) and finally decomposing at $150\,^{\circ}C$ to $200\,^{\circ}C$ to get the pure metal.
$(ii)$ Heating the sulphide ore in air until a part is converted to oxide and then further heating in the absence of air to let the oxide react with unchanged sulphide.
$(iii)$ Electrolysing the molten electrolyte containing approximately equal amounts of the metal chloride and $CaCl_2$ to obtain the metal.
The processes used for obtaining sodium,nickel and copper are,respectively,

Electrometallurgical process is used to extract

In metallurgy,flux is used to: