Question

Atomic number of chlorine is 17. How many electrons are present in the M shell of a chlorine atom?

• A. 2
• B. 7
• C. 4
• D. 8

Answer 1

The correct option is B 7

The maximum number of electrons that can be accommodated in $n^{th}$ shell of an atom is given by $2n^2$.
$$\begin{array}{ccc}\text{Shell}& \text{n}& \text{Maximum no. of electrons}\\ \text{K}& \text{1}& \text{2}\\ \text{L}& \text{2}& \text{8}\\ \text{M}& \text{3}& \text{18}\end{array}$$
Electrons are filled from the inner shell to the outer shell. Number of electrons in chlorine atom = 17 and, electron distribution is given below -
$$\begin{array}{ccc}\text{Shell}& \text{n}& \text{Maximum no. of electrons}\\ \text{K}& \text{1}& \text{2}\\ \text{L}& \text{2}& \text{8}\\ \text{M}& \text{3}& \text{7}\end{array}$$

After complete filling of K and L shell, the remaining seven electrons are filled in shell M. Hence, seven electrons are present in the M shell of the chlorine atom.