Question

A neutral atom of an element has 2K, 8L and 5M electrons. What is the total number of unpaired electrons?

• A. 2
• B. 3
• C. 4
• D. 5

Answer 1

The correct option is B 3

The number of electrons in the shells is given as 2 in K shell, 8 in L shell and 5 in the M shell.

Thus, the atom has in total of 2+8+5 = 15 electrons.

Hence, the atom is phosphorus.

The electronic configuration will be as follows :

$1s^{2}2s^{2}2p^{6}3s^{2}3p^3$

Number of unpaired electrons = 3 $(3p_{x}3p_y$ $3p_z$)
The three unpaired electrons are in the $3p_x,3p_y,$ $3p_z$ orbitals respectively.

Hence, option $\left(B\right)$ is correct.