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

The correct option is C $9.033\times {10}^{23}$
$Z_{eff}$ for HCP electrons $=6$

Number of unit cells in HCP $=\frac{0.5}{6}\times 6.022\times {10}^{23}=\frac{6.022\times {10}^{23}}{12}$

In one unit cell $12$ tetrahedral and $6$ octahedral voids are present.

Total voids $=18$ (in one unit cell)

Total number of voids $=18\times \frac{6.022\times {10}^{23}}{12}=9.033\times {10}^{23}$