Question

Sort the following subshells in the order in which they are filled with electrons.

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

Answer 1

When electrons are added to the subshells of the atoms, they are filled in the order from subshells of lower energy to those of higher energy. The following image shows the order in which the energy of various subshells increases.
(the direction of arrow head indicates the order)

Therefore, the correct order is:
2p < 3s < 3p < 4s < 3d