Question

An atom, X, consists a total number of 9 electrons. So, its outermost orbit _______ will have ______ electrons in it.

• A. M; 8
• B. M; 7
• C. L; 8
• D. L; 7

Answer 1

The correct option is D L; 7

The maximum number of electrons in each orbit is given by $2$ $\times$ $n^2$, where 'n' is the orbit number.

So,
$$\begin{array}{cc}\text{Orbit}& \text{Maximum number of electrons}\\ \text{K}& \text{2}\\ \text{L}& \text{8}\\ \text{M}& \text{18}\\ \text{N}& \text{32}\end{array}$$

The filling of electrons takes place in a step-wise manner. So, firstly inner shells are filled.

9 electrons can be distributed in the orbits in the following manner:
K-shell = 2 electrons
L-shell = 7 electrons

Hence, L is the outermost orbit, and the number of electrons present in it is 7.