* Identify the elements: BaSO3 contains Barium (Ba), Sulfur (S), and Oxygen (O).
* Count the subscripts:
* There's no subscript after Ba, meaning there's 1 barium atom.
* There's no subscript after S, meaning there's 1 sulfur atom.
* The subscript after O is 3, meaning there are 3 oxygen atoms.
Therefore, there are a total of 5 atoms in BaSO3.
