Determine if the electron configurations are valid or invalid

1. A (valid)

2. B (Invalid)

3. B (Invalid)

4. A (valid)

5. B (Invalid)

Explanation:

Electronic configuration:

The electronic configuration is the arrangement of electrons in orbitals (s, p, d, f, g, h so on) according to quantum number and Aufbau rule.

An atom of element have orbitals, and electrons are revolving in it.

There are quantum numbers that describe the number of electron in specific shell.

The Principle quantum number is denoted by "n" and can not be "0".

These "n" is K, L, M, N and electrons are distribution in it.

K =2

L= 8

M= 18

According to Aufbau electron occupied in the lowest energy level before occupying the highest energy level.

According to this the electronic configuration is

1s², 2s², 2p⁶ and so on

So,

"s" orbital accommodate maximum of 2 electrons

"p" orbital accommodate maximum of 6 electrons

"d" orbital accommodate maximum of 10 electrons

"f" orbital accommodate maximum of 14 electrons

and the coefficient 1, 2, 3, 4 are energy level of orbitals.

The 1st orbital is 1s and it only can occupy 2 electrons the next coming electron goes into 2s that also can occupy 2 electrons and the further electrons will go to 2p orbital.

So keeping in mind all above details we investigate all option one by one

1. A (valid)

1s², 2s², 2p⁶, 3s², 3p⁶, 4s², 3d¹⁰, 4p⁵

This is valid option. number of electrons are rightly accommodated in orbitals. Also 3d is higher energy level than 4p.

2. B (Invalid)

1s², 2s², 2p⁶, 3s², 3p⁷

This is invalid option. number of electrons are not rightly accommodated in orbitals as "p" orbital can only accommodate 6 electrons and not more than 6.

3. B (Invalid)

[Xe], 7s², 6d¹, 5f⁸

This is Invalid option. Number of electrons are not rightly accommodated in orbitals. There should 5f orbital before 6d.

4. A (valid)

[Kr] 5s², 4d¹⁰, 5p⁵

This is valid option. number of electrons are rightly accommodated in orbitals.

5. B (Invalid)

1s², 2s², 2p⁶, 3s³, 3p⁶, 4s², 3d¹⁰, 4p⁶, 5s

This is invalid option. number of electrons are not rightly accommodated in orbitals. As "s" can accommodate only 2 electrons not 3 electrons. also there is no details of 5s

i think   the answer is c hope i'm right

atomic mass = 39

number of neutrons = 20

number of protons= 19

electronic configuration = 1s2 2s2 2p6 3s2 3p6 4s1

the number of electron in first shell = 2

number of electrons in n=3 shell = 8