"All gases have the same number of moles in the same volume at constant temperature and pressure:. This statments belongs to :

Avogadro's law (sometimes referred to as Avogadro's hypothesis or Avogadro's principle) is an experimental gas law relating volume of a gas to the amount of substance of gas present.
Avogadro's law states that, "equal volumes of all gases, at the same temperature and pressure, have the same number of molecules".
For a given mass of an ideal gas, the volume and amount (moles) of the gas are directly proportional if the temperature and pressure are constant.