To calculate the number of atoms in 2 moles of aluminum, it is necessary to use the Avogrado constant.
Avogadro's constant is the number of elementary entities contained in 1 mol whose value is 6.02 x 10^23 mol^-1.
So you can just use the rule of three to find the answer:
1.00 mol of aluminum ------ 6.02 x 10^23 mol^-1 atoms of aluminum
2.00 moles of aluminum ----- x atoms of aluminum
x = 2.00 x 6.02 x 10^23
x = 1.20 x 10^24
Answer: There are 1.20 x 10^24 atoms of aluminum