Question

How many total atoms are in 0.320 g of P2O5?

Answer 1

Molar mass of $P_2O_5=142 gm$

Number of moles of $P_2O_5 \ in \ 0.320 \ gm=\frac{0.32}{142}$

Number of atoms in $P_2O_5 \ sample=7 \times N_A\times \frac{0.32}{142}=9.5\times 10^{21}$

Where $N_A$ is avagadro number($6.023 \times 10^{23})$