Given the reaction at equilibrium:H2(g) + Br2(g) <--> 2 HBr(g), Rate of the forward reaction is

Hello thereone of the following properties was originally used to arrange elements on the periodic table, but is no longer used to organize the modern version. which property fits this description? answer: atomic mass  was originally used to arrange elements on the periodic table, but is no longer used to organize the modern version.

If this is a true or galse then its true but if not then what is the question?