Question

Which atom in the ground state has a stable valence electron configuration?
(1) Ar (2) Al (3) Si (4) Na

Answer 1

(1) Ar is your answer. Argon is a noble gas, which is stable in its standard valence electron configuration because it already completed its valence shell following the octet rule.

Answer 2

Answer: (1) Ar

Explanation: Argon is an element with atomic number of 18. Thus it contains 18 electrons. It's electronic configuration in ground state is:

$1s^22s^22p^63s^23p^6$

As argon contains completely filled orbitals, it is stable and is a inert element.

Aluminium is an element with atomic number of 13. Thus it contains 13 electrons. It's electronic configuration in ground state is: $1s^22s^22p^63s^23p^1$

Silicon is an element with atomic number of 14. Thus it contains 14 electrons. It's electronic configuration in ground state is: $1s^22s^22p^63s^23p^2$

Sodium is an element with atomic number of 11. Thus it contains 11 electrons. It's electronic configuration in ground state is: $1s^22s^22p^63s^1$