for every 1 mole of Cu3(PO4)2, there are 2 moles of phosphorus. We also know that 1 mole of Cu3(PO4)2 has 6.022 x 10^23 atoms (Avogadro's number
8.90 moles Cu3(PO4)22 moles P1 mol Cu3(PO4)21 mol Cu3(PO4)26.022 x 10^23 atoms
(53.5958 x 10^23)/2 = 26.7979 x 10^23 atoms of P