Extraction of gold $(Au)$ involves the formation of complex ions $X$ and $Y$ as shown in the reaction: $\text{Gold ore}$ $\xrightarrow{CN^-, H_2O, O_2} HO^- + X$ $\xrightarrow{Zn} Y + Au$. $X$ and $Y$ respectively are:

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,

In smelting,the substance added to combine with impurities to form a molten product is called what?

Limestone is used as a flux in the extraction of

In the electrolysis of alumina to obtain aluminium metal,cryolite is added mainly to

Which metal is leached from its ore using $KCN$?