How many moles is 4.5 x 1021 atoms? !

The number of moles in a substance indicates the amount of the substance that contains the same number of particles as 12 g of the Carbon-12 isotope [or equivalent to 6.02 × 10²³] (which is used as a standard in the world of moles).

Now,

          if     6.02 × 10²³ atoms are found in 1 mole
   then let    4.5 × 10²¹ atoms are found in     x

⇒     x  =    (4.5 × 10²¹)  ÷  (6.02 × 10²³)

            =  0.00748 mol

∴ 4.5 x 10²¹ atoms has in ~ 0.00748 moles