Which element has the electron configuration of argon (Ar) when it has a stable electron

Question

configuration?
(1 point)
potassium (K)
oxygen (O)
magnesium (Mg)
bromine (Br)

Answer 1

The element that has the electron configuration of argon (Ar) when it has a stable electron configuration is potassium (K).

Potassium (K) has an atomic number of 19. Its electron configuration is $[Ar],4s^1$. When potassium loses one electron to become a stable ion (K⁺), it achieves the electron configuration of argon, which is $[Ar]$.

The other elements mentioned (oxygen, magnesium, and bromine) do not achieve the electron configuration of argon as stably as potassium does when they form their ions.