In 1811, Amedeo Avogadro, a famous Italian scientist, suggested that equal volumes of all gases at the same temperature and pressure contain the same number of atoms/molecules. This suggestion is now known as Avogadro's Principle. Avogadro had no idea what the number was. It was after his death that the idea of a mole was introduced and the number of atoms/molecules in one mole is called Avogadro Number. Thus, the number was never actually determined by Avogadro himself. However, experiments based on his principle eventually led to the discovery that there are 6.02 X 1023 atoms/molecules in 22.4 litres of gas at 0°C and 1 atmospheric pressure.
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