Showing that air contains about one-fifth oxygen
2 marks · NormalState the names and approximate percentages by volume of the two most abundant gases present in dry air.
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Nitrogen (about 78%), Oxygen (about 21%)
Also accept: Nitrogen: 78%, Oxygen: 21%; Nitrogen about 4/5, Oxygen about 1/5
Common mistakes: Including water vapour as main component; Incorrect percentages
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Marking points
B1 · 1 mark · Nitrogen stated as the most abundant gas with percentage (accept either ~78% or about 4/5 or 'most').
B2 · 1 mark · Oxygen stated as second most abundant gas with percentage (accept either ~21% or about 1/5).
Worked solution
The two most abundant gases in dry air are nitrogen (about 78%) and oxygen (about 21%).