Total number of voids in 0.5 mole of a compound forming hexagonal closed packed structure are

eff Z for HCP =6 Number of unit cells in HCP = 23 23 0.5 6.022 10 6.022 10 6 12 x x x In one unit cell 12 tetrahedral and 6 octahedral voids are present. Total voids = 18 Total number of voids 23 23 6.022 10 18 9.033 10 12 x x x Hence the correct answer is option (c)