What electron configuration represents an excited state?
An excited state means that (typically) the valence electron has moved from its ground state orbital (i.e. lowest available energy) to some other higher energy orbital.
So any electron configuration in which the last electron (again, the valence electron) is in a higher energy orbital, this element is said to be in an excited state.
For example, if we look at the ground state (electrons in the energetically lowest available orbital) of oxygen, the electron configuration is