Explain Avogadro's Law with the help of a figure.

(N/A) In $1811$,Avogadro proposed that equal volumes of gases at the same temperature and pressure should contain an equal number of molecules.
Avogadro made a distinction between atoms and molecules,which is well-understood in modern times.
If we consider the reaction of hydrogen and oxygen to produce water,we observe that two volumes of hydrogen combine with one volume of oxygen to yield two volumes of water vapor without leaving any unreacted oxygen.
In the figure,each box contains an equal number of molecules. Avogadro explained this result by considering the molecules to be polyatomic. Specifically,he proposed that hydrogen and oxygen exist as diatomic molecules.
At that time,Dalton and others believed that atoms of the same kind could not combine,and thus molecules of oxygen or hydrogen containing two atoms did not exist. However,Avogadro's hypothesis successfully explained the experimental observations.