What does the number below each element's symbol represent? A. The average number of isotopes
B. The average atomic mass
C. The average atomic number
D. The average mass of the ions

14 days is the half-life of phosphorus-32

pv=nrt

explanation:

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.