Here's how to determine the number of atoms in calcium hydroxide, Ca(OH)₂:

* Calcium (Ca): There is 1 calcium atom.

* Oxygen (O): There are 2 oxygen atoms (from the subscript "2" outside the parentheses).

* Hydrogen (H): There are 2 hydrogen atoms (from the subscript "2" inside the parentheses).

Total: 1 + 2 + 2 = 5 atoms