Question

${\text{Mg}}$ can be obtained:
A. By heating ${\text{MgC}}{{\text{l}}_{\text{2}}}$ (anhydrous) with ${\text{Na}}$ in the atmosphere of coal gas.
B. By electrolysis of fused carnallite.
C. By electrolysis of aqueous solution of carnallite.
D. None of the above.

Answer 1

Hint: The elements having reduction potential greater than the reduction potential of hydrogen give the same results for electrolysis in fused and aqueous states. The reduction potential of magnesium is $ - 2.36{\text{ V}}$.

Complete step by step answer:
-When anhydrous magnesium chloride is heated with sodium metal in the atmosphere of coal gas produces magnesium.
The reaction is,
${\text{MgC}}{{\text{l}}_{\text{2}}} + {\text{2Na}}\xrightarrow{{{\text{Heat}}}}{\text{Mg}} + {\text{2NaCl}}$
Thus, heating anhydrous ${\text{MgC}}{{\text{l}}_{\text{2}}}$ with ${\text{Na}}$ in the atmosphere of coal gas gives magnesium.
-Fused carnallite is ${\text{KCl}} \cdot {\text{MgC}}{{\text{l}}_{\text{2}}} \cdot {\text{6}}{{\text{H}}_{\text{2}}}{\text{O}}$. The electrolysis of fused carnallite gives magnesium at cathode and chlorine gas at anode.
Thus, electrolysis of fused carnallite gives magnesium.
-The elements having reduction potential greater than the reduction potential of hydrogen give the same results for electrolysis in fused and aqueous states.
The reduction potential for magnesium is less than the reduction potential of hydrogen. Thus, electrolysis of aqueous solution of carnallite does not give magnesium.
Thus, the correct options are option (A) and option (B).

Note: The tendency of a species to gain or lose electrons and thus get reduced or oxidized respectively is known as the reduction potential.