4. When an aqueous solution suspected of containing Ba2+ or Pb2+ or both is mixed with sulfuric acid a precipitate forms. In another test, when the original solution is mixed with an
aqueous solution of sodium sulfide no precipitate forms. What do these two tests indicate
about the likely presence of Ba2+ and Pb 2+ in the original solution? Explain your answer.

answer: atomic mass was originally used to arrange elements on the periodic table, but is no longer used to organize the modern version.

explanation:

originally atomic mass was used to arrange elements on the periodic table from left to right in a row. each column then shows similar properties of elements of a group.

in modern periodic table, the atoms are arranged in increasing atomic number. as atomic number represents the number of protons in an atom which is unique for every atom.