The answer is 
. A magnesium atom has 12 protons and an arrangement of [2, 8, 2]. When you lose two electrons, arrangement becomes [2,8] and the atom becomes a positively charged ion
I believe the answer is compound B may have a lower molecular weight compared to compound A.
At the same temperature, lighter particles of a compound have a higher average speeds than do heavier particles of another compound. Thus, particles of compound B are lighter than those of compound A and thus they have a higher average speed, hence evaporating faster compared to compound A.
No atoms are lost or made during the chemical reaction so the total mass of the products is equal to the total mass of the reactants. In an atom, protons and neutrons contribute to the mass and since the number of them doesn’t change, the mass doesn’t either.
