Isotopomers are chemically identical molecules that differ in the atomic mass of one or more of atoms of their molecules. In nature, chlorine and bromine both occur in the form of two stable isotopes${ }^{35}\mathrm{Cl}{\text{ and }}^{37}{\mathrm{Cl} }^{81}\mathrm{Br}{\text{, and }}^{79}\mathrm{Br}$. A mixture of gaseous bromine atoms and chlorine atoms are allowed to cool in closed container. Atomic mass is equal to mass number for bromine and chlorine. Atomic mass of Na= 23 and O=16