The element with the lowest atomic mass in Group 2 (alkaline earth metals) on the periodic table is Beryllium (Be).

Here's why:

* Atomic mass increases as you go down a group on the periodic table. This is because the number of protons and neutrons in the atom increases.

* Group 2 includes Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), Barium (Ba), and Radium (Ra).

* Beryllium has the smallest number of protons and neutrons, making it the lightest element in Group 2.