Which energy sublevel occurs out of place because of its lower energy? A. 1p B. 4s C. 2s D. 3d

When arranged in order of increasing energy, the 2s energy sublevel is out of place.

Note: 1p energy sublevel does not exist in the first shell, as there is only the 1s orbital, and this shell can have a maximum of only 2 electrons.

Explanation:

The arrangement of electrons in orbits or shells around the nucleus of an atom is known as the electronic configuration of the atom. Some principles and rules guide electron-filling in atoms; one of which is the Aufbau principle.

According to Aufbau principle, electrons are fed into shells of lower energy levels before filling up of higher energy shells.

The energy levels of of electron orbitals arranged in the order of increasing energy level is given below:

1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, ..., 7p

Therefore, during electron filling, the 2s orbital is filled first before the 4s orbital because it is at a lower energy level.