Thanks all for the help
I have a similar question to this one which says this:
Oxides of the Third Period include:
So in this case it is MgO2 is the incorrect one because Mg = +2 and O = -2 therefore should be Mg2O2 right?
While the others are correct since:
Na = +1, O = -2 therefore Na2O
Al = +3, O = -2 therefore Al2O3
Cl = -1, +1, -3, -5, -7, 0 = -2, therefore Cl2O7
SiO2 is a bit hard because Si has a valency of 4 since it is a element in group 4 so how come it is SiO2 and Not Si2O4?
So which one is wrong SiO2 or MgO2? I say MgO2 but not sure why