Question

The correct ground state configuration of Kr is:

• A. [Ar]344
• B. [Ar]344
• C. [Ar]443
• D. [Ar]344

Answer 1

The correct option is D

[Ar]344

The order in which the orbitals are filled is as follows:

1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s

Maximum number of electrons in s, p, d and f subshells are 2, 6, 10 and 14 respectively.
Now let's write the electronic configuration of [Ar].
Atomic Number of Ar is 18.
[Ar] = 1$s^2$ 2$s^2$ 2$p^6$ 3$s^2$ 3$p^6$

Now by following Aufbau Principle, Pauli's exclusion principle and Hund's Rule, we can easily write the configuration.

Atomic number of Kr is 36.

Kr=[Ar]4$s^2$ 3$d^{10}$ 4$p^6$