For this problem, to determine the number of moles given the number of atoms, we use the Avogadro's number. This is an empirical value that relates the number of particles (e.g. atoms, molecules, sub-particles) in one mole of any substance. The value is 6.022×10²³ atoms/mol.
3.90×10²⁴ atoms * 1 mol/6.022×10²³ atoms = 6.476 moles of Aluminum
