Bromine-$79$ and bromine-$81$ are found in nature in the ratios $50.69$ and $49.31$. What will be the average atomic weight of bromine?

Write the rules proposed for electron distribution under the Bohr-Bury scheme. Use the rules to write the electronic configuration of given atoms. Also, give the number of neutrons present in each atom.

${}_9{}^{19}\mathrm{F}, {}_{12}{}^{24}\mathrm{Mg}, {}_{14}{}^{28}\mathrm{Si}, {}_{15}{}^{31}\mathrm{P}, {}_{17}{}^{35}\mathrm{Cl}$