Showing that air contains about one-fifth oxygen
2 marks · NormalName two gases that together make up almost all of dry, unpolluted air, and state their approximate combined percentage by volume.
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Nitrogen and oxygen; together about 99%
Also accept: Nitrogen and oxygen, 99%; Nitrogen & oxygen, together 99%
Common mistakes: Omitting percentage; Naming argon or carbon dioxide
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Marking points
B1 · 1 mark · States both nitrogen and oxygen.
B2 · 1 mark · Gives combined percentage as about 99%.
Worked solution
Nitrogen and oxygen together make up about 99% of dry, unpolluted air.