Answer:
Ba, or Barium
Explanation:
Alkaline Earth Metals are in the 2nd group of the Periodic Table.
Be
Mg
Ca
Sr
Ba
Ra
These are the Alkaline Earth metals. They start on Period 2:
Period 2 - Be
Period 3- Mg
Period 4 - Ca
Period 5 - Sr
Period 6 - Ba
Period 7 - Ra
