To determine the number of atoms in a given amount of a substance, you can use Avogadro's number (6.022 x 10^23 atoms/mol).
In this case, you have 7.3289 x 10^2 moles of nickel (II) dihydrogen phosphite. To find the number of atoms, you can multiply the number of moles by Avogadro's number:
Number of atoms = (7.3289 x 10^2 mol) * (6.022 x 10^23 atoms/mol)
Calculating this expression gives:
Number of atoms = 4.40924 x 10^26 atoms
Therefore, you have approximately 4.40924 x 10^26 atoms of nickel (II) dihydrogen phosphite.