Whose law states that equal volumes of gas contain equal numbers of molecules?

Amedeo Avogadro, an Italian scientist, proposed that equal volumes of gases at the same temperature and pressure contain equal numbers of molecules. He stated the idea in 1811, though it was not widely accepted until later. The principle is fundamental to chemistry because it connects gas volume with the amount of substance. It also helped distinguish atoms from molecules in the development of atomic theory. The constant associated with his name is central to modern chemistry and the mole concept.