1. Understand Electron Configurations:

* Na (Sodium): [Ne] 3s¹ (Sodium has one valence electron in the 3s orbital)

* Cl (Chlorine): [Ne] 3s² 3p⁵ (Chlorine has seven valence electrons)

2. Ion Formation:

* Na⁺ (Sodium ion): Loses its one valence electron, resulting in [Ne] electron configuration.

* Cl⁻ (Chloride ion): Gains one electron, resulting in [Ar] electron configuration.

3. Noble Gas Resemblance:

* Na⁺ has the same electron configuration as Neon (Ne).

* Cl⁻ has the same electron configuration as Argon (Ar).

Conclusion:

* Na⁺ resembles Neon in its electron configuration.

* Cl⁻ resembles Argon in its electron configuration.

This is why these ions are considered to be stable and unreactive, like the noble gases.