Here's how to figure out the number of sulfur atoms in aluminum sulfate:

1. Chemical Formula:

* Aluminum sulfate has the chemical formula Al₂(SO₄)₃.

2. Subscripts:

* The subscript "3" outside the parentheses means there are three sulfate (SO₄) groups.

* The subscript "4" within the parentheses indicates there are four oxygen atoms in each sulfate group.

3. Total Sulfur Atoms:

* Since there are three sulfate groups and each group has one sulfur atom, there are a total of 3 * 1 = 3 sulfur atoms in aluminum sulfate.