B

X-rays are produced primarily due to changes in atomic energy levels.
When an electron transitions between different energy levels in an atom, energy is emitted in the form of X-rays if the transition involves the inner electron shells.
During processes such as electron bombardment, when electrons collide with target atoms, they can knock out inner-shell electrons. The vacancy created then leads to transitions of electrons from higher energy levels to fill the lower energy vacancy, emitting X-rays in the process.
Therefore, the correct explanation is that X-rays are produced through changing atomic energy levels.