Answer and explanation:
The mole ratio for Mg and MgO would be 2:2 or 1:1 because Mg has 2 as a coefficient and so does MgO, which is why you can simplify the ratio to 1:1
The mole ratio for O and MgO would be 1:2 because O has 1 as the coefficient and MgO has 2 as a coefficient.
