-
Notifications
You must be signed in to change notification settings - Fork 0
/
Copy pathfile_out.html
1 lines (1 loc) · 4.56 KB
/
file_out.html
1
<html><p><b style="color:#ff0000">Oxygen</b> is a <b style="color:#ff0000">chemical</b> <b style="color:#ff0000">element</b> with symbol O and <b style="color:#ff0000">atomic</b> <b style="color:#ff0000">number</b> 8 . </p><p>It is a member of the chalcogen group on the <b style="color:#ff0000">periodic</b> <b style="color:#ff0000">table</b> and is a highly reactive nonmetallic element and oxidizing agent that readily forms compounds ( notably oxides ) with most elements . </p><p>[ 1 ] By mass , <b style="color:#ff0000">oxygen</b> is the third-most abundant element in the universe , after hydrogen and helium . </p><p>[ 2 ] At STP , two atoms of the element bind to form dioxygen , a diatomic gas that is colorless , odorless , and tasteless , with the formula O 2 . </p><p>Many major classes of organic molecules in living organisms , such as proteins , nucleic acids , carbohydrates , and fats , contain <b style="color:#ff0000">oxygen</b> , as do the major inorganic compounds that are constituents of animal shells , teeth , and bone . </p><p>Most of the mass of living organisms is <b style="color:#ff0000">oxygen</b> as it is a part of water , the major constituent of lifeforms ( for example , about two-thirds of human body mass ) . </p><p>Elemental <b style="color:#ff0000">oxygen</b> is produced by cyanobacteria , algae and plants , and is used in <b style="color:#ff0000">cellular</b> <b style="color:#ff0000">respiration</b> for all complex life . </p><p><b style="color:#ff0000">Oxygen</b> is toxic to obligately anaerobic organisms , which were the dominant form of early <b style="color:#ff0000">life</b> <b style="color:#ff0000">on</b> <b style="color:#ff0000">Earth</b> until O 2 began to accumulate in the atmosphere . </p><p>Free elemental O 2 only began to accumulate in the atmosphere about 2.5 <b style="color:#ff0000">billion</b> <b style="color:#ff0000">years</b> <b style="color:#ff0000">ago</b> during the <b style="color:#ff0000">Great</b> <b style="color:#ff0000">Oxygenation</b> <b style="color:#ff0000">Event</b> , about a <b style="color:#ff0000">billion</b> <b style="color:#ff0000">years</b> after the first appearance of these organisms . </p><p>[ 3 ] [ 4 ] Diatomic <b style="color:#ff0000">oxygen</b> gas constitutes 20.8 % of the volume of air . </p><p>[ 5 ] <b style="color:#ff0000">Oxygen</b> is the most abundant element by mass in the <b style="color:#ff0000">Earth</b> <b style="color:#ff0000">'s</b> <b style="color:#ff0000">crust</b> as part of oxide compounds such as silicon dioxide , making up almost half of the <b style="color:#ff0000">crust</b> <b style="color:#ff0000">'s</b> mass . </p><p>[ 6 ] <b style="color:#ff0000">Oxygen</b> is an important part of the atmosphere , and is necessary to sustain most terrestrial life as it is used in respiration . </p><p>However , it is too chemically reactive to remain a free element in <b style="color:#ff0000">Earth</b> <b style="color:#ff0000">'s</b> <b style="color:#ff0000">atmosphere</b> without being continuously replenished by the photosynthetic action of living organisms , which use the energy of sunlight to produce elemental <b style="color:#ff0000">oxygen</b> from water . </p><p>Another form ( allotrope ) of <b style="color:#ff0000">oxygen</b> , <b style="color:#ff0000">ozone</b> ( O 3 ) , strongly absorbs UVB <b style="color:#ff0000">radiation</b> and consequently the high-altitude <b style="color:#ff0000">ozone</b> <b style="color:#ff0000">layer</b> helps protect the biosphere from <b style="color:#ff0000">ultraviolet</b> <b style="color:#ff0000">radiation</b> , but is a pollutant near the surface where it is a by-product of smog . </p><p>At even higher <b style="color:#ff0000">low</b> <b style="color:#ff0000">earth</b> <b style="color:#ff0000">orbit</b> altitudes , atomic <b style="color:#ff0000">oxygen</b> is a significant presence and a cause of erosion for spacecraft . </p><p>[ 7 ] <b style="color:#ff0000">Oxygen</b> is produced industrially by <b style="color:#ff0000">fractional</b> <b style="color:#ff0000">distillation</b> of liquefied air , use of zeolites with pressure-cycling to concentrate <b style="color:#ff0000">oxygen</b> from air , <b style="color:#ff0000">electrolysis</b> of <b style="color:#ff0000">water</b> and other means . </p><p>Uses of elemental <b style="color:#ff0000">oxygen</b> include the production of steel , plastics and textiles , brazing , welding and cutting of steels and other metals , rocket propellant , <b style="color:#ff0000">oxygen</b> therapy and <b style="color:#ff0000">life</b> <b style="color:#ff0000">support</b> systems in aircraft , submarines , spaceflight and diving . </p></html>