0.5 moles of ${\mathrm{P}}_4{\mathrm{O}}_{10}$ contains

0.5 mole of ${\mathrm{P}}_4{\mathrm{O}}_{10}$ contains

0.5 × 10 × 16 = 80 g of oxygen

0.5 × 4 gram atoms of P = 2g atoms of P

5 g atoms of oxygen.