The correct ground state configuration of Kr is:
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] = 1s2 2s2 2p6 3s2 3p6
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]4s2 3d10 4p6