Consider the following metallurgical processes :

(P) Heating impure metal with CO and distilling the resulting volatile carbonylte.p. 43° C) and finally decomposing at 150°-200° C to get the pure metal.

(Q) 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 metal sulphide.

(R) Electrolysis of the molten electrolyte containing approximately equal amounts of the metal chloride and NaCl to obtain the metal.

The processes used for obtaining magnesium, nickel and copper are respectively:

Down's technique involves electrolyzing the molten electrolyte (NaCl) containing $CaC{l}_2$.

Calcium chloride and potassium fluoride together raise the melting point of NaCl from ${800}^{\circ }\mathrm{C}\text{ to }{1600}^{\circ }\mathrm{C}$ degrees Celsius. At the cathode, which is an iron rod, sodium is obtained. The anode is a rod of graphite.

To get pure nickel metal, an impure metal must be heated with CO, distilled from the resultant volatile carbonyl, and then decomposed between ${150}^{\circ }\mathrm{C}\text{ to }{230}^{\circ }\mathrm{C}$. The sulfide ore is heated in the presence of oxygen until some of it is transformed into oxide, and then it is heated once again without oxygen to let the oxide combine with the remaining sulfide to produce copper metal.

$\begin{array}{l}2{\mathrm{Cu}}_2\mathrm{S}+3{\mathrm{O}}_2\to 2{\mathrm{Cu}}_2\mathrm{O}+2{\mathrm{SO}}_2\\ 2{\mathrm{Cu}}_2\mathrm{O}+{\mathrm{Cu}}_2\mathrm{S}\to 6\mathrm{Cu}+{\mathrm{SO}}_2\end{array}$

This is an illustration of auto reduction, and the technique is known as besemerization.

It takes 3, 1, and 2 processes, respectively, to produce sodium, nickel, and copper.

Hence Correct option is C