oxygen + oxides

Question 1

how much nitrogen is in the air

Answer 1

78%

Question 2

how much oxygen is in the air

Answer 2

21%

Question 3

how much argon is in the air

Answer 3

0.96

Question 4

how much carbon dioxide is in the air

Answer 4

0.04%

Question 5

how to measure percentage of oxygen in air

Answer 5

by reacting with another element
then taking initial volume of air away from final