Question

what is aufbau's principle? can anyone please explain me.

Answer 1

In the building up of atoms, the electrons enter the various orbitals, in the increasing order of their energies based on (n+1) rule.
1s< 2s < 2p < 3s < 3p < 4s < 3d........

Answer 2

states that in the ground state of an atom ,an electron enters the orbital of lowest energy first and. subsequent electrons are fed order of increasing energies

I hope it helps:)