How many moles of Pb are in 4.71 × 10^21 Pb atoms?

0.00782 mol Pb

Explanation:

There are always 6.02 × 10²³ atoms in 1 mole of an element.

4.71 × 10²¹ atoms Pb × (1 mol Pb ÷ 6.02 × 10²³ atoms) = 0.00782 mol Pb

alchemy hadn't scientific methods of study, appeal to mysticism and fantasy, the knowledge of chemistry and physics were modest at that time.

alchemy was - but as new rules were discovered it either changed into chemistry or it became "unscientific".