Question

An atom has 2 electrons in K shell, 8 electrons in L shell and 8 electrons in M shell. The number of s electrons present in the element is:
A. 10
B. 7
C. 6
D. 4

Answer 1

Hint: electronic configuration: It is the arrangement of electrons in the sequential order in the respective shells. The basic electronic configuration of order \[2,8,8,16,32,64\]
And the advanced configuration follows: \[1s,{\text{ }}2s,{\text{ }}2p,{\text{ }}3s,{\text{ }}3p,{\text{ }}4s,{\text{ }}3d,{\text{ }}4p,{\text{ }}5s,{\text{ }}4d,{\text{ }}5p,{\text{ }}6s,{\text{ }}4f,{\text{ }}5d,{\text{ }}6p,{\text{ }}7s,{\text{ }}5f,{\text{ }}6d\]

Complete step by step solution:
If we see the electronic configuration sequence \[1s,{\text{ }}2s,{\text{ }}2p,{\text{ }}3s,{\text{ }}3p,{\text{ }}4s,{\text{ }}3d,{\text{ }}4p,{\text{ }}5s,{\text{ }}4d,{\text{ }}5p,{\text{ }}6s,{\text{ }}4f,{\text{ }}5d,{\text{ }}6p,{\text{ }}7s,{\text{ }}5f,{\text{ }}6d\]firstly the electrons need to be filled in the lower shells, having least energies and when they will be complete and no more addition of electrons can occur, the filling of the next shell will be done. As we can see the 4s orbital comes before 3d because it has lower energy than 3d orbital and the filling and the removal of electrons firstly takes place from 4s orbital.
$ K{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;L{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;M \\
  2{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;8{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}8 \\
    \\
$
Thus, the atomic number of the element will be: 2 + 8 + 8 = 18
And electronic configuration of the element will be as follows: $[1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}]$
Thus, the total number of s electrons in the atom of argon is 6

So, the correct answer is Option C.

Note: Argon is the noble gas because it has complete electronic configuration and does not need to accept the electrons from any other element to complete its orbital. Due to its complete shells it shows the inert nature of the argon gas.

The electronic configuration imparts various properties to the element like melting and boiling point, the ability to lose or gain electrons to get stable, the atomic radii of elements or its ability to interact with other elements of the periodic table. As the atomic number increases the nuclear charge increases and the size of the atom decreases as we move along the period because the electrons are added in the same shell and the nuclear pull increases, but there is different trend down the group the size increases because the number of shells