Here's how to determine the number of atoms in 3CaCl₂:

* Break down the formula: 3CaCl₂ means there are 3 units of calcium chloride (CaCl₂).

* Atoms per unit: Each unit of CaCl₂ contains:

* 1 calcium atom (Ca)

* 2 chlorine atoms (Cl)

* Total atoms:

* Calcium atoms: 3 units * 1 Ca atom/unit = 3 Ca atoms

* Chlorine atoms: 3 units * 2 Cl atoms/unit = 6 Cl atoms

* Grand total: 3 Ca atoms + 6 Cl atoms = 9 atoms

Therefore, there are 9 atoms in 3CaCl₂.