In 1811, Avogadro, an Italian physicist, advanced the hypothesis that equal volumes of gases under identical conditions of pressure and temperature contain the same number of molecules. Now one of the fundamental concepts of the atomic theory of matter, his theory has become known as Avogadro’s law. Since then, physicists have determined the number of molecules in the gram-molecular weight and found that it is the same for all gases. This number, called Avogadro’s number, is how large? Discuss
Source: The Free Dictionary