Answer is: C. nitrogen.
Together, nitrogen (N₂) and oxygen (O₂) by volume account for 99.03% volume of the gases composing the dry air in the lower atmosphere.
Volume of nitrogen in air is 78.08%.
Volume of oxygen in air is 20.95%.
Together: 78.08% + 20.95% = 99.03%.
This gases can be separated by fractional distillation of liquefied air .