How many atoms of gold (Au) are present in a sample of 2.5 mol Au? A. 1.5 * 1024 atoms Au B. 1.5 * 1023 atoms Au C. 4.2 * 1024 atoms Au D. 4.2 * 1023 atoms Au

The answer is A. 1.5 * 1024 atoms Au.

To calculate this, we will use Avogadro's number which is the number of atoms in 1 mole of substance:

6.02 * 10²³ units per 1 mole

So, we need a proportion:

If 6.02 * 10²³ atoms are in 1 mole, how many atoms will be present in 2.5 moles:

6.02 * 10²³ atoms : 1 mole = x : 2.5 mol

After crossing the products:

1 mole * x = 2.5 moles * 6.02 * 10²³ atoms

x = 2.5 * 6.02 * 10²³ atoms

x = 15.05 * 10²³ atoms = 1.505 * 10²⁴ atoms = 1.5 * 10²⁴ atoms