Volume % = mole %
Molar mass of oxygen = 32kg/kmol
Molar mass of nitrogen = 28 kg/kmol
Density of nitrogen = Density of oxygen x molar mass of oxygen x molar ratio of air x molar mass of nitrogen
Density of nitrogen = (1.43kgm^-3)(1 kmol O2/32 kg O2)(80 kmol N2/ 20 kmol O2)(28 kg N2/1 kmol O2) = 5.01 kg/m3