Final answer:
When an electron in an atom moves from a higher energy state, it emits a photon.
Step-by-step explanation:
An electron in an atom moves from a higher energy state. When it transitions to a less excited state or the ground state, it emits a photon. This is because the electron releases the energy it gained when it transitioned to the higher energy state. Therefore, the correct answer is A) It emits a photon.