Why do not we use `MgCI_(2)` instead of `CaCI_(2)` to lower the melting point of NaCI in the Down's process?

Explanation

If `MgCI_(2)` is used to lower the melting point of `NaCI`, the `Mg^(2+)` ions will be discharged at cathode instead of `Na^(+)` ions because `E^(@)` valu of `Mg^(2+)//Mg` is more (-2.37) than that of `na^(+)//Na` (-2.87 V). But `CaCI_(2)` can be safely used since the `E^(@)` value of `Ca^(2+)//Ca` (-2.90 V) is less than that of sodium. Thus, there is no chance of `Ca^(2+)` ions getting liberated at the cathode in preference to `Na^(+)` ions.