Please assist with the following quantum chemistry question

Cr(oh)3 -> cr(3+) + 3oh-

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.

It will appear as o2(g) as a reactant