When a nonmetal blank valence electrons it becomes negatively charge. This is a particular type od ion called

It will appear as o2(g) as a reactant 

Mars contains iron oxide in its crust

Iwould have to say

It depends on how many moles there are, if you have about 4 moles you must divide that number by 2.5 and add 14 to it and you will get your answer.