According to the following Ellingham diagram,$A$ reduces $BO_{2}$ when the temperature is

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,

Write the chemical reactions involved in the extraction of gold by the cyanide process. Also,explain the role of zinc in this extraction.

Cryolite is

In the manufacture of iron,limestone is added to the blast furnace. The calcium ion ends up in the form of:

In the extraction of copper from copper pyrites,iron is removed as