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Oxygen is a normally gaseous, nonmetallic chemical element with the symbol O and the atomic number 8. It is widely prevalent in the earth's atmosphere, in which it is essential for the respiration of humans and other living creatures. It is also widely prevalent across 70 percent of the earth's surface in the form of water (H2O), of which the most important compound is oxygen.

Oxygen was discovered in the 18th century by Joseph Priestley in England, Carl Wilhelm Scheele in Sweden, and Antoine Lavoisier in France, working independently. Lavoisier was responsible for identifying oxygen as an element and determining its role in combustion, which had previously been attributed to the phenomenon of phlogiston.

Oxygen constitutes approximately 0.03 percent of all atoms in the universe, which makes ...

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