Question

Which of these elements doesn't have a fully filled K amd M shells outer shell?

• A. Helium
• B. Neon
• C. Hydrogen
• D. Argon

Answer 1

The correct option is C Hydrogen

$\bullet$ The maximum electrons that a shell can accommodate is given by $2n^2$, where n is the shell number.

$\bullet$ So, the maximum numbers of electrons that K, L and M shells can accommodate are 2, 8 and 18 respectively.
$$\begin{array}{ccc}\text{Element}& \text{Atomic No.}& \text{Electronic Configuration}\\ \text{Helium}& \text{2}& \text{2}\\ \text{Neon}& \text{10}& \text{2,8}\\ \text{Hydrogen}& \text{1}& \text{1}\\ \text{Argon}& \text{18}& \text{2,8,8}\end{array}$$
$\bullet$ Hence, hydrogen does not has fully filled K shell
$\bullet$ and argon does not has fully filled M shell