If 1/4 of the parent isotope is left in the rock how many half-lives have passed? 1
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GIVING BRAINLIEST TO WHOEVER HAS THE RIGHT ANSWER

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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.