Heating a mixture of $Cu_2O$ and $Cu_2S$ will give

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,

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

In the extraction of which of the following metals is a complex salt formed?

Which of the following chemical equations represents the hydrometallurgical process for the extraction of copper from its ore?

The slag consists of molten impurities generally in the form of