Question

The change of an atom from the excited state to the ground state always requires _______

Answer 1

Answer: emission of electromagnetic radiation

Explanation:

When an atom is in its ground state, its electrons fill the lower energy orbitals completely before they begin to occupy higher energy orbitals.  

On the other hand, when an atom is excited (it has left its ground state, in which each electron occupies its place in its orbit, around the nucleus),  some electron jumps out of the orbit it occupied in its fundamental state to an outer orbit, further away from the nucleus and then return to the ground state, emitting in the form of electromagnetic radiation (light which may be visible or not) the energy received.  

So, when an excited electron passes from an outer orbit to the ground state, it produces electromagnetic radiation of a specific wavelength that depends on the amount of energy the electron releases in the process.

Therefore:

The change of an atom from the excited state to the ground state always requires the emission of electromagnetic radiation.