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A colourless, odourless gaseous element belonging to group 16 of the periodic table. It is the most abundant element present in the earth's crust. It also makes up 20.8 percent of the Earth's atmosphere. For industrial purposes, it is separated from liquid air by fractional distillation. It is used in high temperature welding, and in breathing. It commonly comes in the form of Oxygen, but is found as Ozone in the upper atmosphere. It was discovered by Priestley in 1774.
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