2. The diagram below represents the bright-line spectra of four elements and a bright-line spectrum
produced by a mixture of two of these elements.
Which two elements are in this mixture?
(1) barium and hydrogen
(2) barium and lithium
(3) helium and hydrogen
(4) helium and lithium

you didnt put any of the following

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.