• Oxygen organised in molecules of three oxygen atoms rather than the usual two
  • A poisonous and highly reactive blue gas whose chemical formula is O3, making it an allotropic form of oxygen. It may be formed, for instance, when oxygen is exposed to electrical discharges, or in certain photochemical reactions. Ozone has a characteristic odor, which is sometimes detected near a lightning stroke, and although it is toxic, a layer of ozone in the atmosphere helps shields living organisms from excessive ultraviolet radiation from the sun.

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