Question

Which noble gas has only two electrons in its valence shell?

• A. Radon
• B. Krypton
• C. Neon
• D. Helium

Answer 1

The correct option is D

Helium

Explanation for correct option (D):

• Helium has two electrons in its valence shell having the atomic number $2$ and its electronic configuration is called duplet configuration.
• Helium has the electronic configuration $2$.
• It has only two electrons in its valance shell.

Explanation for incorrect options:

(A) Radon: Radon is a noble gas having an atomic number $86$. it has an octet configuration. It has total $8$ electrons in its valence shell.

(B) Krypton: Krypton has an octet configuration. It has total $8$ electrons in its valence shell. Krypton has the atomic number $36$.

(C) Neon: Neon has an octet configuration. It has total $8$ electrons in its valence shell. The atomic number of Neon is$10$.

Hence, option (D) is correct. i.e., Helium has only two electrons in its valence shell.