There is an unknown container of metal(M) in the stockroom. To determine the metal’s identity, the following galvanic cell was constructed at 25°C:M(s) ǀ M2+(aq, 0.747 M) ‖ Au3+(0.0496 M) ǀ Au(s) If the measured cell potential is 4.388 V, what is the identity of the unknown metal? The metal is an alkaline earth metal, this information should help.

Half-Reaction E° (V)
Au3+ + 3e-→ Au +1.498
Be2+ + 2e-→ Be -1.847
Mg2+ + 2e-→ Mg -2.372
Ca2+ + 2e-→ Ca -2.868
Sr2+ + 2e-→ Sr -2.890
Ba2+ + 2e-→ Ba -2.912
Ra2+ + 2e-→ Ra -2.920

the seeing the electronic configuration we can say that the element is fluorine.

fluorine is the most electronegative element in the periodic table.

but by only seeing the configuration we cannot say about its reactivity because we don't know if its configuration after excitation or by addition of electrons.

but if not then, it is the lightest halogen and exists as a highly toxic pale yellow diatomic gas at standard conditions. as the most electronegative element, it is extremely reactive: almost all other elements, including some noble gases, form compounds with fluorine.