Which electron configuration represents the electrons in an atom of chlorine in an excited state?
(1) 2-7-7 (3) 2-8-7
(2) 2-7-8 (4) 2-8-8

Electron transfiguration shows the arrangement of electrons in the energy levels.
atomic number of chlorine is 17
The electron configuration of Cl in the ground state is 2,8,7
To become stable Cl should have a complete octet , Cl has 7 electrons in the outermost shell and it needs to one more electron to become stable
Therefore it takes in one electron becomes stable
Then electron configuration in excited state is
2,8,8
Answer is 4)2,8,8