Which electron configuration represents an atom in an excited state (i.e., an electron has been promoted to a higher-energy orbital while a lower-energy orbital is not filled as expected in the ground state)?

• A. $1s^{2}2s^{2}2p^{6}3s^1$
• B. $1s^{2}2s^2$
• C. $1s^{2}2s^{1}2p^1$
• D. $1s^{2}2s^{2}2p^1$

Answer: (C)