Question

Which of the following orbital will be filled first?

• A. 4s
• B. 4p
• C. 3d
• D. 5s

Answer 1

The correct option is A

4s

In the ground state of atoms, the orbitals are filled in the increasing order of energies. In other words, electrons first occupy the lowest energy orbital available to them and then enter into higher energy orbitals only after the lower energy orbitals are filled.

The order in which the energies of the orbitals increase or 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.....