To prevent magnesium from oxidation in the electrolytic extraction process, which of the following is done?
A. Some calcium fluoride is added.
B. Some metal chlorides are added.
C. Metal is taken out by spoons.
D. The whole process is done in an atmosphere of coal gas.

Answer
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Hint: Magnesium is retrieved by electrolytic decomposition of anhydrous magnesium chloride. The process of extraction of metals by electrolysis of the fused is called electrometallurgy. Electrons work as the reducing agent.

Complete Step by Step Solution:
Metals are extracted from their fused salt by the process of electrometallurgy. Electrons serve as the reducing agent in this process. The process of obtaining Mg from magnesium chloride is called the Dow process. This fused magnesium chloride is obtained from brine and seawater.

The salt undergoes electrolysis in the molten state.
Cathode: The \[{\rm{M}}{{\rm{g}}^{{\rm{2 + }}}}\] ion undergoes reduction by two electrons to magnesium metal.
\[{\rm{M}}{{\rm{g}}^{{\rm{2 + }}}}{\rm{ + 2}}{{\rm{e}}^{\rm{ - }}} \to {\rm{Mg}}\]
Anode: Each pair of \[{\rm{C}}{{\rm{l}}^{\rm{ - }}}\] ions undergoes oxidation to form chlorine gas losing two electrons.
\[{\rm{2C}}{{\rm{l}}^{\rm{ - }}}\left( {{\rm{aq}}} \right) \to {\rm{C}}{{\rm{l}}_{\rm{2}}}\left( {\rm{g}} \right){\rm{ + 2}}{{\rm{e}}^{\rm{ - }}}\]

We can see that Mg is formed by undergoing reduction. But it tends to lose electrons and undergo oxidation sometimes.
We have to find out the process used to prevent magnesium from oxidation in the electrolytic extraction.
A. Some calcium fluoride is added.
Calcium fluoride is added to the fused salt to increase its electrical conductivity and reduce the melting point.
So, A is incorrect.

B. Some metal chlorides are added.
This process does not prevent magnesium from oxidation.
So, B is incorrect.

C. Metal is taken out by spoons.
This process does not prevent magnesium from oxidation.
So, C is incorrect.

D. The whole process is done in an atmosphere of coal gas.
The electrolysis is accomplished in an atmosphere of coal gas to prevent oxidation and loss of heat due to radiation.
So, option D is correct.

Note: A saline solution containing Mg2+ ions is initially reacted with lime forming the magnesium hydroxide as a precipitate. The hydroxide is then treated with hydroxide with hydrochloric acid and heated to form magnesium chloride.