NaCl has 2 atoms, one of Na (sodium) and one of Cl (chlorine) The chemical formula says that there are 12 molecules of NaCl present so if there are 2 atoms in each molecule of NaCl, there are 24 atoms present.
Na-1 atom, Cl-1 atom, NaCl-2 atoms, 3 NaCl - 6 atoms There is one atom in the atom Na. There is one atom in the atom Cl. There are 2 atoms in the ionic compound NaCl. There are 6 atoms in the 3 NaCl ionic compounds. (Just thought I would clarify.)