Question

18.0 grams of oxygen is reacted with nitrogen to make 56.0 grams of nitrogen dioxide according to the following reaction:
2O2 + N2 ---> 2 NO2
How much nitrogen (in grams) reacted?

Answer 1

There is something inconsistent about your numbers. You need more than 18 g of O2 to make 56 g of NO2. The stoichiometry does not match up.

Check your numbers again.