Here's how to break down the calculation to determine the number of atoms in 3 Ca(NO3)2:

1. Understanding the Formula:

* Ca(NO3)2: This represents one formula unit of calcium nitrate.

* Ca: Calcium (1 atom per formula unit)

* N: Nitrogen (2 atoms per formula unit, since it's inside parentheses and the subscript is 2)

* O: Oxygen (6 atoms per formula unit, 3 from each nitrate group)

2. Total Atoms per Formula Unit:

* 1 (Ca) + 2 (N) + 6 (O) = 9 atoms per formula unit

3. Calculating Atoms in 3 Formula Units:

* 9 atoms/formula unit * 3 formula units = 27 atoms

Therefore, there are 27 atoms in 3 Ca(NO3)2.