The bohrs bury scheme says that 2n^2 where n is the energy level is used to find the electrons on a shell but it also says that the maximum number of electrons on the outermost shell is 8

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.  

its b it was a compound