Fe2+(s) + Cr6+(aq) → Fe3+(aq) + Cr3+(aq) Which element is being reduced?
Which element is being oxidized?
Which reactant is the reducing agent?
Which reactant is the oxidizing agent?

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.