Here's how to determine the total number of atoms in magnesium hydroxide (Mg(OH)₂):

* Identify the elements: Magnesium hydroxide contains magnesium (Mg), oxygen (O), and hydrogen (H).

* Count the atoms of each element:

* There is 1 magnesium atom (Mg).

* There are 2 oxygen atoms (O).

* There are 2 hydrogen atoms (H).

* Add the atoms together: 1 + 2 + 2 = 5

Therefore, there are a total of 5 atoms in a molecule of magnesium hydroxide.