Noble Gases' Unique Electron Configurations

Steps:

• Noble gases are chemically inert due to full valence electron shells, preventing reactions.
• Xenon, in period 5, has 8 electrons in its outer shell (5s²5p⁶ configuration).
• Helium, in period 1, has a full outer shell with only 2 electrons (1s² configuration), as the first shell holds a maximum of 2.
• Both elements share inertness but not the octet rule exactly, as helium follows the duet rule.

Why B is correct:

• Noble gases achieve stability via complete valence shells per the octet (or duet for He) rule, making them inert; helium's K-shell holds 2 electrons, not 8.

Why the others are wrong:

• A: Incorrect, as helium has 2 valence electrons, not 8.
• C: Incorrect, as both helium and xenon are chemically inert.
• D: Incorrect, as both helium and xenon are chemically inert.

Final answer: B