The right answer is that Joseph Priestly would be considered an inorganic chemist, because oxygen is an element which is the object of study of inorganic chemistry. On the other hand, biochemists study the biomolecules (molecules involved in life); organic chemists study organic molecules (molecules with C, H and other elements); and physical chemistry is a complex field that study the matter based on chemical and physics concepts, it includes electrochemistry, thermodynamic, and quantum physics, among others.