Which of the following is represented in the highest percentage by volume in dry air?
a. oxygen
b. carbon dioxide
c. nitrogen
d. hydrogen

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 .

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