Question

complete the table

fill - in order	subshell
8th	----
7th	----
6th	----
5th	----
4th	----
3rd	----
2nd	----
1st	----

choose
5s
4s
4p
2d
3d
3s
2s
3p
4d
1p
2p
1s

Explanation:

Step1: Recall electron - filling order

The electron - filling order is based on the Aufbau principle, which states that electrons fill the lowest - energy orbitals first. The order of filling is 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p, etc.

Step2: Match fill - in order with subshell

1st: 1s
2nd: 2s
3rd: 2p
4th: 3s
5th: 3p
6th: 4s
7th: 3d
8th: 4p
9th: 5s

Answer:

Fill - in order	Subshell
8th	4p
7th	3d
6th	4s
5th	3p
4th	3s
3rd	2p
2nd	2s
1st	1s