Dow's process of extraction of Mg involves extraction of Mg from sea water. Sea water is concentrated in sun-light and is then treated with slaked lime. Magnesium hydroxide is heated in a stream of HCl to give `MgCl_(2)` which is electrolysed to discharge Mg. The mixture is in the ratio 35% `MgCl_(2)+50% NaCl+15% CaCl_(2)`. NaCl and `CaCl_(2)` are added to lower the fusion temperature and to increases the conductance.
`Mg^(2+) +Ca(OH)_(2) to Mg(OH)_(2)+Ca^(2+)`
`Mg(OH)_(2)+2HCl to MgCl_(2)+2H_(2)O(l)`
Electrolysis of fused `MgCl_(2) hArr Mg^(2+)+2Cl`
`Mg^(2+)+2e^(-) to Mg`( At Cathode)
`2Cl^(-) to Cl_(2)+2e^(-)` (At Anode)
Mg electrolysed is protected from atmospheric oxidation by a blanket of inert gases.
Molten mixture contains `Mg^(2+), Na^(+) and Ca^(2+)` but at cathode only `Mg^(2+)` is discharged because :

Options

A. Standard reduction potential of `Mg` is least among the three
B. Standard oxidation potential of `Mg` is least among the three
C. Discharge potential of `Mg` is highest
D. None of these

Answer

B