An elemental crystal has a density of 8570 kg / ^ 3 . The packing...

The packing efficiency $=0.68$, means the given lattice is $\mathrm{BCC}$. The closest distance of approach $=2 \mathrm{r}$$\begin{array}{l}2 r=2.86 A=a \sqrt{3}\\ \text{ or a }=\frac{2 \times 2.86}{\sqrt{3}}=3.30 Ã… \end{array}$Let atomic weight of the element $=\mathrm{a}\begin{aligned} \therefore \frac{2 \times 9}{36 \times 10^{23} \times(3.3)^{3} \times 10^{-24}}=8.57 \\ \mathrm{a}&=8.57 \times3 \times(3.3)^{3} \times0.1 \\ \text{ and } =92.39 \simeq 93 \mathrm{amu} \end{aligned}$$$