11 mark
Clean air contains oxygen, nitrogen, carbon dioxide and some noble gases. Which row correctly states the percentages of each gas present in clean, unpolluted air?
| % O2 | % N2 | % CO2 & noble gases |
A | 20 | 78 | 2 |
B | 21 | 78 | 1 |
C | 19 | 79 | 2 |
D | 20 | 79 | 1 |
Choose your answer