This is the 3100th most frequent Russian word.
кислорода
Oxygen.
The word 'кислорода' is used in its genitive case form to express lack or absence.
Человек не может долго жить без кислорода.
A person cannot live long without oxygen.
The word 'кислорода' is related to its role in essential processes, here in nominative case for the subject.
Для дыхания и горения необходим кислород.
Oxygen is necessary for breathing and combustion.
The word 'кислорода' is used in a scientific context, specifying its proportion in the atmosphere.