State the percentage of oxygen found in dry air.
Carbon dioxide is removed from a sample of air by passing the air through aqueous sodium hydroxide. Explain why aqueous sodium hydroxide is able to remove carbon dioxide from air.
Describe how oxygen, nitrogen and the noble gases are separated from one another after carbon dioxide has been taken out.
Describe how oxygen is tested. test observed result
Ozone, $\text{O}_3$, is produced in the atmosphere when nitrogen dioxide reacts with oxygen in the presence of ultraviolet light. State the type of chemical reaction that occurs during the formation of ozone in this way.
Nitrogen dioxide is produced in internal combustion engines. State one further atmospheric source of nitrogen dioxide.
A layer of ozone is found high in the atmosphere. State one problem for humans that can occur if the ozone layer is depleted by CFCs.