Which action will slow down the rate of a reaction? a. decreasing surface area of a solid reactant b. adding a catalyst to the reaction c. increasing the concentration of the reactants d. raising the temperature of the reactants

answer; 4 electrons;

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.