Which of the following is not correctly matched with respect to the processes involved in the extractive metallurgy of the respective metal ?

Options

A. `Al_(2)O_(3).2H_(2)OrarrAl:` Leaching, precipitation, calcination and electrolytic reduction (molten state).
B. `Ag_(2)S rarrAg:` Leaching and displacement method.
C. `PbSrarr Pb:` Froth flotation process, roasting and self reduction.
D. `KCl.MgCl_(2).6H_(2)O rarr Mg :` Dehydration by simple heating electrolytic reduction in aqueous phase.

Answer

4

Explanation

`(1)Al_(2)O_(3)(s)+3H_(2)O(l)+2NaOH(aq)overset("Leaching")rarr2Na[Al(OH)_(4)](aq)`
`2Na[Al(OH)_(4)](aq)+CO_(2)(g)rarrAl_(2)O_(3).xH_(2)O(s)+2NaHCO_(3)(aq)`
`Al_(2)O_(3).xH_(2)O(s)underset("Calcination")overset(1470K)rarrAl_(2)O_(3)(s)+xH_(2)O(g)`
Electrolytic reduction of molten pure `Al_(2)O_(3)` mixed with `Na_(3)AIF_(6)` or `CaF_(2)`
Method is known as Hall-Heroult process
Cathode`:" "Al^(3+)("melt")+3e^(-)rarrAl(l)`
Anode`:" "C(s)+O^(2-)("melt")rarrCO(g)+2e^(-)`
`C(s)+2O^(2-)("melt")rarrCO_(2)(g)+4e^(-)`
`(2)` Leaching `:`
`Ag_(2)S+4NaCNhArr 2Na[Ag(CN)_(2)]+Na_(2)S`
`Na_(2)S+2O_(2)rarr Na_(2)SO_(4)`
Displacement by zinc in aqueous solution `:`
`2Na[Ag(CN)_(2)]+ZnrarrNa_(2)[Zn(CN)_(4)]+2Agdarr`
`(3)` Roasting `:`
`2PbS+3O_(2)overset(Delta)rarr2PbO+2SO_(2)`
Self reduction `:`
`2PbO+PbS rarr 2Pb+SO_(2)`
`(4)` Calcination `:`
`MgCl.6H_(2)Ounderset("Dry "HCl(g))overset(Delta("calcination"))rarrMgCl_(2)+6H_(2)O`
It is not made anhydrous by simple heating because because it gets hydrolysed.
`MgCl_(2).6H_(2)Ooverset(Delta)rarrMgO+5H_(2)O+2HCl`
Electrolytic reduction `:`
Electrolytic reduction of molten anhydrous camallite.
`MgCl_(2)hArr Mg^(2-)+2Cl^(-)`
At cathode `: Mg^(2+)+2e^(-)rarr Mg(99%"pure"),`
At anode `: 2Cl^(-) rarrCl_(2)+2e^(-)`