Answer;
(4) 2-8-8
Explanation;
An electron configuration shows the arrangement of electrons around the nucleus of an atom. At the ground state (the most stable state for electrons) the electron configuration of chlorine is 2-8-7. Chlorine is a halogen that contains 17 electrons, to attain a stable configuration chlorine requires to gain 1 electron.
-At the excited state chlorine will therefore have an electron configuration of 2-8-8.