How many electrons are transferred in the reaction between magnesium metal and oxygen? Give your answer as a ratio of moles of electrons to moles of magnesium.
2Mg(s) + O2(g) ==> 2MgO
For Mg, each Mg atom changes oxidation state from 0 to +2 for a total of 4 electrons. Each oxygen atom changes oxidation state from 0 to -2 for a total of 4 electrons. So you have 4 mols of electrons/2 mols Mg or 2/1.