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Consi der the following metallurgical processes
$(I)$ Heating impure metal with $CO$ and distilling the resulting volatile carbonyl (b.p. $43\,^oC$ ) and finally decomposition at $150^o-200\,^oC$ 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 metal sulphide
$(III)$ Electrolysis of the molten electrolyte containing approximately equal amounts of the metal chloride and $NaCl$ to obtained the metal
The processes used for obtaining magnesium, nickel and copper are respectively
$(I),\,(II)$ and $(III)$
$(II),\,(III)$ and $(I)$
$(III),\,(I)$ and $(II)$
$(II),\,(I)$ and $(III)$
Solution
$(I)$ $\mathop {\operatorname{Ni} }\limits_{(impure)} + 4{\text{CO}}\xrightarrow{{50\,{\,^o}C}}$ $\mathop {\left[ {{\text{Ni}}\left( {{\text{C}}{{\text{O}}_4}} \right)} \right]}\limits_{(volatile)} \xrightarrow{{230\,{\,^o}C}}\mathop {{\text{Ni}}}\limits_{(pure)} + 4{\text{CO}} \uparrow $
$(II)$ ${\text{C}}{{\text{u}}_2}{\text{S}} + \frac{3}{2}{{\text{O}}_2}\xrightarrow{\Delta }{\text{C}}{{\text{u}}_2}{\text{O}} + {\text{S}}{{\text{O}}_2}$
${\text{C}}{{\text{u}}_2}{\text{S}} + 2{\text{C}}{{\text{u}}_2}{\text{O}}\xrightarrow{{high\,\,temp.}}6{\text{Cu}} + {\text{S}}{{\text{O}}_2}$
$(III)$ ${\text{MgC}}{{\text{l}}_2}_{({\text{s}})}\xrightarrow{{{\text{ electrolysis }}}}{\text{M}}{{\text{g}}^{2 + }}(l) + 2{\text{C}}{{\text{l}}^ – }(l)$
At cathode : ${\text{M}}{{\text{g}}^{2 + }} + 2{{\text{e}}^ – } \to {\text{Mg}}\,({\text{s}})$
At anode : $2{\text{C}}{{\text{l}}^ – }(l) \to {\text{C}}{{\text{l}}_2}(g) + 2{e^ – }$
