Question

A neutral atom of an element has 2K, 8L and 5M electrons. Atomic number of neutral atom is:

• A. 20
• B. 18
• C. 15
• D. 25

Answer 1

The correct option is C 15

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.

This means that the atom is phosphorus.

The electronic configuration will be as follows.

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