Questions & Answers about Oksygenet går gjennom røret.
Because Norwegian usually marks the by attaching an ending to the noun.
- rør = tube / pipe
- røret = the tube / the pipe
The same happens with oksygen:
- oksygenet = the oxygen
The ending -et is the definite singular ending for many neuter nouns.
Yes, oksygenet is the definite form.
This can feel a little unusual to English speakers because English often uses substance words with no article, like oxygen, water, air, and so on. Norwegian can also do that in some contexts, but when you are talking about a specific oxygen supply, stream, or amount already understood from the situation, oksygenet is very natural.
So in this sentence, oksygenet most likely means the oxygen being discussed.