Selection Rule of electron transition :-
If a photon light of the right frequency is absorbed by an electron,the electron jump to a higher frequency,if the electron releases a photon of light it will be jump to a lower energy state.
Certain transitions are more likely to occur than others.The ones that have a high probability of a occurring are called the allowed transition while the ones that are less likely take place are called forbidden transitions.
In quantum mechanics a set of rule exist known as the selection rule that and the allowed transition
These rules tell us that electron cannot jump between two orbitals that differs by more than one orbital quantum number.
From the selection rule the electron can jump from any of 2P orbital to 2s orbital
But notice that electron cannot jump between two P orbital because Δl= 0.