Number of atoms in hcp (hexagonal close packaging =1 mole 1 mole has 6.023×1023 particles. No. of tetrahedral voids =2× no. of atoms in closed packaging =2×6.022×1023 No. of octahedral voids = no. of atoms in closed packaging =6.023×1023 Total no. of voids = tetrahedral + octahedral voids ‌‌=(2×6.023×1023)+(6.022×1023) ‌‌=12046×1023+6.023×1023 ‌‌=18.049×1023=1.8×1024