In which principal energy level and sublevel is the unpaired

electron that forms the covalent bond for Cl2?

3p^5

Principal energy level=3

Sublevel = p

Explanation:

Chlorine has the complete electronic configuration 1s2 2s2 2p6 3s2 3p5. Now the outer most shell ns2 np5 for halogens is now 3s2 3p5 for chlorine. Since the p-sub level has three degenerate orbitals, namely; px, py, pz; in filling five electrons into these degenerate orbitals, two occupy the px, two occupy the py and the remaining one electron occupies the pz. This is the unpaired electron that goes into covalent bonding to firm the chlorine molecule. Hence the answer given above.