<u>Answer:</u> 0.275 moles of oxygen gas is consumed in the reaction.
<u>Explanation:</u>
We are given:
Moles of magnesium = 0.550 moles
For the given chemical reaction:

By Stoichiometry of the reaction:
2 moles of magnesium reacts with 1 mole of oxygen gas.
So, 0.550 moles of magnesium will react with =
of oxygen gas.
Hence, 0.275 moles of oxygen gas is consumed in the reaction.