Answer 1

Explanation of Gay -Lussac's Law: Gay -Lussac had experimentally determined that one volume of hydrogen and one volume of chlorine react to produce two volumes of hydrogen chloride gas.
According to Avogadro's law, if :
1 volume of hydrogen contains n molecules of the gas then 1 volume of chlorine also contains n molecules of the gas. Therefore 2 volume of hydrogen chloride
contain 2n molecules of the gas.
H₂ + Cl₂ → 2HCI
1 vol 1 vol  2 vol    (by Gay -Lussac)
n          n      2n        (By Avogadro)

but hydrogen and chlorine are diatomic.
So, 2 atoms + 2 atoms →  2 molecules
1 atom + 1 atom → 1 molecu le
i .e. 1 molecule of hydrogen chloride is formed when 1 atom of hydrogen combines with 1 atom of chlorine. Thus Avogadro's law explains Gay -Lussac's law of
combining volumes.