Concept:Nitrogen prepared from air is not absolutely pure because it may retain some atmospheric impurities, but oxygen is never one of them since it is removed during the process.
Explanation:Nitrogen is usually obtained from air after oxygen has been removed.
The nitrogen collected still contains small amounts of carbon(IV)oxide, water vapour, and inert gases such as argon.
These gases remain mixed with nitrogen and make it impure.
Oxygen, however, has already been removed, so it is not present as an impurity in the nitrogen obtained.
Therefore, oxygen is the component that nitrogen does not contain.
Answer:A. oxygen