An atom is excited when electrons are boosted from the ground state (where they have the lowest amount of energy) to an excited state (when they have more than that). This can be done using heat, light, or by adding electricity.
It’s this excitation that makes fluorescent light bulbs work. When electricity is added, the atoms gain energy and the electrons jump to an excited state. When they fall back down to the ground state, they give off the excess energy as light.
As for what is the specific excited state for an atom, that would depend on the atom and the number of electrons. There’s no one answer for this, and more information is needed.
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