* The subscript: The subscript "2" after the "OH" in the formula Ba(OH)₂ indicates that there are two hydroxide (OH) groups.
* Oxygen in each group: Each hydroxide group (OH) contains one oxygen atom.
* Total oxygen atoms: Since there are two hydroxide groups, the total number of oxygen atoms is 2 groups * 1 oxygen atom/group = 2 oxygen atoms.
Therefore, there are two oxygen atoms in one unit of Ba(OH)₂.
