Question

Which atom in the ground state has a stable valence electron configuration?

(1) Ar (2) Al (3) Si (4) Na

Answer 1

Answer: (1) Ar

Step-by-step 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`

Answer 2

(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.