Here's how to determine the number of oxygen atoms in barium hydroxide:

1. Chemical Formula:

* Barium hydroxide has the chemical formula Ba(OH)₂.

2. Subscripts:

* The subscript "2" after the parentheses indicates that there are two hydroxide (OH) groups in each molecule of barium hydroxide.

3. Total Oxygen Atoms:

* Each hydroxide group contains one oxygen atom.

* Since there are two hydroxide groups, there are a total of 2 * 1 = 2 oxygen atoms in each molecule of barium hydroxide.