An atom has an atomic number of 9 a mass number of 19 and an electron configuration of 2-6-1 explain why the number of electrons in the second and third shells shows that this is in an excited state

You can tell that the atom is in the excited state because:

- Electron configuration should follow the 2-8-8-2 rule, meaning that the inner shell should be filled before the next shell can start holding electrons.

- Instead of the atom's electron configuration being in the ground state at 2-8-8-1, electrons from the second shell have jumped to the third.