Oxygen
Oxygen is a gaseous element common in the atmosphere of class M planets, although at relatively low levels (about 20% on Earth, for example).

Oxygen was vital for the survival of most carbon-based lifeforms. Some lifeforms, however, had adapted to go without oxygen for extended periods of time, such as Fantome from , who had a very large lung capacity. ()

In 2258 of the alternate reality,  reminded  that his crew did not require oxygen to survive as 's did, being kept in stasis, and it would involve merely cutting off their life support systems to kill them all. ()

One of the tests given at Starfleet Academy involved working in an atmosphere that was oxygen deficient. Choriocytosis produced similar symptoms to the conditions of the test. () 

During a scan of Aldean DNA, Doctor Beverly Crusher was able to confirm that a drop in atmospheric O2 was not responsible for the Aldeans' sterility. ()

One species, the Benzites, could not breathe the oxygen-nitrogen atmosphere deemed "normal" by most Federation species. ()

When Kira Nerys and Doctor Julian Bashir beamed aboard the Kobliad transport Reyab, Bashir noted that the vessel's O2 pressure levels were dropping. ()

In 2369 the runabout  returned from a routine mission in the Gamma Quadrant to Deep Space 9 due to a power failure, their life support and oxygen levels dropped dangerously low. ()

After the alien probe "Pup" damaged most of the station's systems in 2369, a plasma fire occurred in a corridor in the habitat ring. Major Kira Nerys gave Lieutenant  the order to bring portable oxygen and something to treat plasma burns. ()

Oxygen was also a critical component of life support functions aboard most space-going craft. In 2374, while playing a hypothetical game with the delusion Trajis Lo-Tarik, Seven of Nine asked him to imagine that the oxygen on the bridge of the  had been depleted and then sealed it with a level 3 force field. Later, Seven cut power to all life support in order to maintain power to the ship's stasis units, and a delusion of Captain Kathryn Janeway commented that without heat and oxygen it was "Goodbye, Seven." ()

Materials containing oxygen 
 carbon dioxide
 carbon monoxide
 clancium oxide
 deuterium oxide
 dilithium hydroxyl
 DNA
 ferric oxide
 hydroxyl
 iridium oxide
 methyl oxide
 nitrogen tetroxide
 nitrogen oxide
 nitrous oxide
 veridium oxide
 water

External link 
 

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Elements