Answer: Im not sure if you are doing this in your class.
Explanation:
So... for the element of MAGNESIUM, you already know that the atomic number tells you the number of electrons. That means there are 12 electrons in a magnesium atom. Looking at the picture, you can see there are two electrons in shell one, eight in shell two, and two more in shell three
Find the molar mass of Fe_2O_3
2Fe = 2*56 = 112
3O = 3* 16 = 48
Molar Mass = 160 grams
moles= given mass / molar mass
moles = 28 / 160
moles = 0.175 <<<< answer
Then I would guess the answer is D because Na2OH is much more common and stable than Na2O is <span />