Which law is illustrated by compounds $\mathrm{H}_2 \mathrm{O}$ and $\mathrm{H}_2 \mathrm{O}_2$ formed from two different elements, H and O ?

What is the volume of oxygen required for complete combustion of 0.25 mole of methane at S.T.P.?

Chlorine exists in two isotopic forms ${ }^{35} \mathrm{Cl},{ }^{37} \mathrm{Cl}$. If average atomic mass of chlorine is 35.5 , what is the percentage abundance of these isotopes respectively?

Chlorine has two isotopes ${ }^{35} \mathrm{Cl}$ and ${ }^{37} \mathrm{Cl}$ with average atomic mass of 35.5 . What is the ratio of their relative abundance respectively?