Question

Which of the following does not belongs to group $18$?

• A. $Kr$
• B. $Xe$
• C. $Rb$
• D. $Rn$

Answer 1

The correct option is C

$\mathrm{Rb}$

Explanation for the correct option:

(C) $\mathbf{Rb}$:

$\mathbf{18}$ group elements:

• The elements of group$18$ are non-reactive and are referred to as noble gases.
• Group$18$ elements should have $8$ electrons in their valence shell, forming an octet with a stable electronic configuration.

Rubidium $\left(\mathrm{Rb}\right)$:

• Rubidium is a chemical element with the symbol $\mathrm{Rb}$.
• It is a group$1$ element and has one valence electron in the valance shell.

Hence, (C) is the correct option.

Explanation for the incorrect options:

Krypton $\left(\mathrm{Kr}\right)$, Xenon $\left(\mathrm{Xe}\right)$, and Radon $\left(\mathrm{Rn}\right)$ belong to group $18$ because they have a stable complete octet. Therefore, options (A), (B), and (D) are incorrect.

Therefore, the correct option is (C) $\mathbf{Rb}$. It does not belong to group $18$.