That law states that 1 MOLE of ANY GAS takes up the same amount of volume at constant temperature and pressure. Assuming 25C and 100 kpa (standard lab conditions), 1 Mole of any gas takes up 24.79L. Unfortunately, you havent specified which reaction between oxygen and nitrogen is occuring so it is hard for me to answer.
However, remember that 2/24.79 L of both element are available to be reacted.