a gas misture containing N2 and O2 was kept inside a 2.00 L container at a temp of 23.0 degrees C and a total pressure of 1.00atm. The partial pressure of O2 was 0.722atm. How many grams of Nitrogen were present in the mixture?

Ptotal = pO2 + pN2. You have Ptotal and pO2, solve for pN2, substitute pN2 for P in PV = nRT and solve for n = number of moles N2. Finally, n = grams/molar mass. Yu have n and molar mass, solve for grams.