Question

A metal $M$ forms hexagonal close-packed structure. The total number of voids in $0.02 \,mol$ of it is ____$\times 10^{21}$ (Nearest integer)
$\left(\right.$ Given $\left.N_A=6.02 \times 10^{23}\right)$

Answer 1

One unit cell of hep contains $=18$ voids
No. of voids in $0.02 \,mol$ of hcp
$ =\frac{18}{6} \times 6.02 \times 10^{23} \times 0.02 $
$ \approx 3.6 \times 10^{22} $
$\approx 36 \times 10^{21}$