To convert a given quantity, in this case number of atoms, to number of moles, you must use Avogadro's number, i.e. 6.022 * 10^23.
1 mol of atoms Al = 6.022 * 10^23 atoms Al
=> 1 = 1 mole atoms Al / 6.022 * 10^23 moles Al
So you have to multiply
4.2 * 10 ^22 atoms Al * 1 mol atoms Al / 6.022 * 10^23 atoms Al
That is the fourth option of your question.
