The table below shows the fossils found in various layers of an undisturbed rock: fossils in rock layers layer (from top) fossil in layer 1 a, c 2 e 3 a, d, f 4 b 5 f, c 6 d, b which is most likely an index fossil?

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.  

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