A) 16g of O atom= NA atoms . Hence 1g of O atom = NA16 atoms=0.0625 atoms
B) 32 g of O2 molecule= 2×NA atoms . Hence 1g of O2 molecule = 2×NA32 atoms=0.0625 atoms
C) 48g of O3 molecule = 3×NA atoms . Hence 1g of O3 molecule = 3×NA48 atoms=0.0625 atoms