Showing that air contains about one-fifth oxygen
1 mark · EasyState the approximate percentage by volume of oxygen in dry air.
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21%
Also accept: 21; 21 percent; about 21%
Common mistakes: 20%; 18%; 23%
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Marking points
A1 · 1 mark · Correctly states that oxygen makes up about 21% of dry air.
Worked solution
The approximate percentage by volume of oxygen in dry air is 21%.