The percentage of the nitrogen gas does not vary between inhaled and exhaled air because nitrogen is not used during respiration. 

Whereas the percentage of oxygen and carbon dioxide varies in the inhaled and exhaled air as gaseous exchange takes place in the alveoli. Oxygen from inhaled air diffuses into the capillaries and carbon dioxide from the capillaries diffuses out into the alveolar air. Thus, the exhaled air has more percentage of carbon dioxide than oxygen.