1) Convert grams of P2O5 into moles of P2O5.
The molar mass of P2O5 is 141.9445 g/mol
[tex]\text{mol of P}_2O_5=0.700gP_2O_5\cdot\frac{1molofP_2O_5}{141.94gP_2O_5}=0.004931molP_2O_5[/tex]2) Convert moles into molecules
[tex]\text{molecules of P2O5=0.004931 mol P2O5}\cdot\frac{6.02\cdot10^{23}\text{molecules}}{1\text{ mol P2O5}}=2.968\cdot10^{21}\text{molecules of P2O5}[/tex]3) Convert molecules into atoms
[tex]numberofatoms=2.968\cdot10^{21}\text{molecules of P2O5}\cdot\frac{7\text{ atoms}}{1\text{ molecule }}=2.0779\cdot10^{22}\text{ atoms}[/tex]There are 2.0779*10^22 atoms in 0.700 g of P2O5.