Which of the following happens when chlorine forms an ion?

a. it gains an electron and has an octet in its outer shell.

b. it loses an electron and has an octet in the next-lowest energy level.

c. it gains an electron and has an octet in the lowest energy level.

d. it loses an electron and has an octet in its innermost shell.

What  happens  when  chlorine  form  an ion  is that  it gains an electron and  has  an octet  in its  outer shell  ( answer  A)

Explanation

Chlorine is  is in atomic  number  17  in periodic table.

The electron configuration  of chlorine  is    1S2 2S2 2P6 3S2 3P5   or[Ne]3S2 3p5  or  2.8.7.

chlorine therefore  has 7 valence electron therefore it  gain  1 electron  to form Cl- ( ion)

Cl- has  8  electron in its outer  shell (  it  obeys  octet  rule  of eight valence in outer shell.