In this task you will be given a text passage from a trivia quiz. You should choose the category this question belongs to from these categories: History, Science, Social Science, Fine Arts, Literature. You can only choose one category, so if in doubt, please choose the closest match.

His rule of greatest simplicity postulated that if two elements form only one compound, than the compound has the simplest composition: one atom of each element. His most famous theory includes Lavoisier's postulate of the conservation of mass and explains Proust's law of definite proportions. His law states that the total pressure of a mixture of gases is the sum of the partial pressures. FTP, name this English chemist who proposed the atomic theory of matter.
Science