Lavoisier discovered oxygen, oxidation and the chemical compound of water. His research refuted the phlogiston theory valid at his time

He determined the Law of Conservation of Mass in 1789: Nothing is created, either in the operations of art or in those of nature, and it may be considered as a general principle that in every operation there exists an equal quantity of matter before and after the operation

Lavoisier was executed during the French Revolution at the guillotine on 8 May 1794.