The correct answer is b. al, mg, li
That's because Cobalt is not a representative element since it's not found in the first 2 or the last 6 groups.
Answer:lhkllknkkknknkknk lhkllknkkknknkknk knkkknknknnkn
lhkllknkkknknkknk knkkknknknnknlhkllknkkknknkknk knkkknknknnkn
Explanation: