Each sulfur ("IV") oxide molecule is capable of accepting two electrons and being reduced. The species that have lost the two electrons is considered "oxidized."
stackrel(+4)("S")"O"_2 + 1/2 color(white)(l) "O"_2 color(white)(l) + 2 color(white)(l) "e"^(-) to stackrel(+6)("S")"O"_3 (g)
Organic molecules tend to lose color on oxidation.
Magnesium "Mg" is a metal and form basic oxides. "MgO" neutralizes hydrochloric acid "HCl", a primary component of the gastric juice, to form "MgCl"_2 and water:
"MgO" (s) + 2 color(white)(l) "HCl"(aq) to "MgCl"_2 (aq) + 2 color(white)(l) "H"_2"O"(l)
Additionally, magnesium "Mg" lies in the third period and tends to be non-toxic at low dosages. "MgO" is generally insoluble in water and will not be directly absorbed if administrated in excess.