To calculate the total number of atoms in C6H4Cl2, we simply add up the number of atoms of each element in the molecular formula.

C6H4Cl2 contains:

- 6 Carbon (C) atoms

- 4 Hydrogen (H) atoms

- 2 Chlorine (Cl) atoms

In total, there are 6 + 4 + 2 = 12 atoms in C6H4Cl2.