Explain how Avogadro hypothesis is used to derive the value of atomicity.

Explanation

( i)The Avogadro.s law states that "equal volumes of all gases under similar conditions of temperature and pressure contain equal number of molecules".
(ii) Let us consider the reaction between hydrogen and chlorine to form hydrogen chloride gas.
`H_(2(g))+Cl_(2(g))+2HCI_((g))`
`1 volume + 1 volume to 2 volumes`
(iii) "According to Avogadro.s law, I volume of any gas is occupied by number of molecules. "
"n" molecules + "n" molecules  `to`"2n" molecules
If "n"= 1, then
  1 molecule + I molecule `to`2 molecules.
`1//2 "molecule" +1//2 "moleculeto molecule"`
  (iv) I molecule of hydrogen chloride gas is made up`1//2` of molecule of hydrogen and`1//2` molecule of chlorine.
(v) molecule of hydrogen contains alumn.So, 1 molecule of hydrogen contains 2 atoms. So, hydrogen atomicity is 2. Similarly chlorine atomicity is also 2. So, `H_(2)` and `Cl_(2)` are diatomic molecules.