Question

Arrange the following orbitals in the increasing order of their energies.

• A. 2s
• B. 2p
• C. 3s
• D. 3p
• E. 4s

Answer 1

As the principle quantum number $(n$) increases, the energy of the orbital also increases.
Electrons are assigned to orbitals in order of increasing value of $n+l$.

If two orbitals have the same $n+l$ value, then the orbital with lower $n$ value will have the lower energy.

Hence, the increasing order of energy of the given orbitals will be:
1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < 4d < 5p...