It is a modification of gay-Lussac’s law.
Avogadro’s Law states that at constant temperature and pressure, equal volume of gases contains the same number of molecules.
V ∝ n
ie. (V1 / n1 ) / (V2 / n2 )
Note: 1MOLE = 22.4 DM3 = 6.02 x 1023 for all gases at Stp.