if not all the magnesium reacts, will the reported magnesium to oxigen ratio be too high or too low?

You could take the numbers from your experiment, decrease the mass of Mg a little and see which way the ratio goes. I think you will find that Mg:O ratio will be too high.

The mass of Mg you weigh to begin is some number. If some fails to react moles Mg will stay the same in your calculatins but mol Oxygen will be less. Mg to O then is larger than 1:1. It may be something like 1:0.8

To determine whether the reported magnesium to oxygen ratio will be too high or too low if not all the magnesium reacts, we need to understand the chemical reaction between magnesium and oxygen.

Magnesium typically reacts with oxygen to form magnesium oxide according to the following balanced chemical equation:

2 Mg + O2 → 2 MgO

This equation shows that for every 2 moles of magnesium reacting, 1 mole of oxygen is needed to produce 2 moles of magnesium oxide.

If not all the magnesium reacts, it means that there is an insufficient amount of oxygen to react with all the magnesium. This could occur, for example, if there is limited oxygen supply or if the reaction is not carried out under ideal conditions.

In such a case, the reported magnesium to oxygen ratio will be higher than the stoichiometric ratio of 2:1. This is because the amount of magnesium that reacted is fixed, but the amount of oxygen used in the reaction is less than the required amount.

Therefore, the reported magnesium to oxygen ratio will be too high if not all the magnesium reacts.