Question

Which of these elements have a fully filled outermost shell?

• A. Hydrogen
• B. Sodium
• C. Neon
• D. Carbon

Answer 1

The correct option is C Neon

$\bullet$ Each shell can accomodate $2n^2$ electrons. Thus, a fully filled first shell has 2 electrons, second shell has 8 electrons and so on.

$\bullet$ Electronic configuration of the elements is given below-
$$\begin{array}{ccc}\text{Atom}& \text{Atomic no.}& \text{Electronic configuration}\\ \text{Hydrogen}& \text{1}& \text{1}\\ \text{Sodium}& \text{11}& \text{2,8,1}\\ \text{Neon}& \text{10}& \text{2,8}\\ \text{Carbon}& \text{6}& \text{2,4}\end{array}$$
Only neon has fully filled outermost shell.