Quantum transitions that result in the characteristic sharp lines of the X-ray spectrum always involve

(A) the inner electron shells
(B) electron energy levels that have the same principal quantum number
(C) emission of beta particles from the nucleus
(D) neutrons within the nucleus
(E) protons within the nucleus

Question

Quantum transitions that result in the characteristic sharp lines of the X-ray spectrum always involve 

(A) the inner electron shells
(B) electron energy levels that have the same principal quantum number
(C) emission of beta particles from the nucleus
(D) neutrons within the nucleus
(E) protons within the nucleus

anonymous · Answer

I would say A, because to transit from one quantum number to the other, it means that we have gone to an inner shell, meaning ionization energy increased blatantly.