The Periodic Table is arranged according to? the number of electrons that each element has.
the boiling point of the elements.
the reactivity of the elements.
the number of protons each element has.

The number of protons each element has.

Explanation:

The number of protons each element has is also known as the atomic number. Elements are arranged from left to right and top to bottom in order of increasing atomic number. The order generally coincides with increasing atomic mass. The rows are called periods.

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.