• 1 a.m.u= 1/12 part of mass  of C-12(a.m.u= atomic mass unit)

Atomic Weight: Atomic weight of an element is a number which indicates how many times its atom is heavier than an atom of hydrogen

• Molecular Weight=Weight of molecule/weight of 1/12 of a carbon atom.

Gay-Lussac's Law: When the gases react they do so in volumes in a whole number ratio keeping temperature and pressure in constant.
Avogadro's Hypothesis: Equal volumes of all gases under the similar gases under the similar conditions of temperature and pressure contain the equal number of molecules.
Applications of Avogadro's Hypothesis:

• It is useful in determining the atomicitys of elementary molecules & formulae of compounds.
  
• To obtain the relationship between vapor density and molecular weight of a substance.
  

​Avogadro Number N= 6.023*10 (power of -23).
Mole: A mole is defined as the quantity of substance which contain the same number of particles as are present in 0.012 KG of pure carbon-12