How many total atoms are in 0.220 g of p2o5?

From the periodic table:

molecular mass of P = 30.9 grams

molecular mass of O = 16 grams

Therefore:

molar mass of P2O5 = 2 (30.9) + 5 (16) = 141.8 grams

Number of moles = mass / molar mass = 0.22/141.8 = 1.55 x 10^-3 moles

One mole of any substance contains Avogadro's number of atoms. Therefore, number of atoms in 1.55 x 10^-3 moles is:

1.55 x 10^-3 x 6.022 x 10^-3 = 9.34 x 10^20 atoms