how did he die?
He contracted a disease of the skin, which, combined with kidney problems caused his death. However, Doctors said he died of Mercury Poisoning
Carl Wilhelm Scheele
In the fall of 1785, Scheele began to suffer from symptoms described as kidney disease. In early 1786, he also contracted a disease of the skin, which, combined with kidney problems, so enfeebled him that he could foresee an early death. With this in mind, he married the widow of his predecessor, Pohl, two days before he died, so that he could pass undisputed title to his pharmacy and his possessions to her.

While Scheele's experiments generated substances which have long since been found to be hazardous, the compounds and elements he used to start his experiments were dangerous to begin with, especially heavy metals. Like most of his contemporaries, in an age where there were few methods of chemical characterisation, Scheele would smell and taste any new substances he discovered. Cumulative exposure to arsenic, mercury, lead, their compounds and perhaps hydrofluoric acid which he had discovered, as well as other substances took their toll on Scheele, who died at the early age of 43, 
where does most of the oxygen come from on earth The most amount of Oxygen comes from photosynthesis, which uses the energy of sunlight to produce oxygen from water and carbon dioxide. when was it discovered? In the year 1773. by whom? It was discovered independently by Carl Wilhelm Scheele, in Uppsala, in 1773 what are it's uses? Low Pressure Breathing gas in Modern Space Suits, Scuba Divers rely on artificially delivered Oxygen & Medically for Oxygen Masks among many other uses. is it toxic? Can be Toxic at elevated partial pressures, leading to convulsions and other health problems. did the one who discovered it publish any paper regarding this? No
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Carl Wilhelm Scheele [SEP] Death
In the fall of 1785, Scheele began to suffer from symptoms described as kidney disease. In early 1786, he also contracted a disease of the skin, which, combined with kidney problems, so enfeebled him that he could foresee an early death. With this in mind, he married the widow of his predecessor, Pohl, two days before he died, so that he could pass undisputed title to his pharmacy and his possessions to her. While Scheele's experiments generated substances which have long since been found to be hazardous, the compounds and elements he used to start his experiments were dangerous to begin with, especially heavy metals.