Regarding graphite the following information is available: 

The density of graphite -2.25 g/cm³. What is C-C bond distance in graphite?

 

Let C-C bond distance in graphite is d $\stackrel{\mathrm{o}}{\mathrm{A}}$

$\begin{array}{l}\text{∴ Surface area }=6\times \frac{\sqrt{3}}{4}\times d^2=6\times \frac{\sqrt{3}}{4}\times d^2\times {10}^{-16}{\mathrm{cm}}^2\\ \therefore \text{ Vol. of the unit cell }=6\times \frac{\sqrt{3}}{4}\times d^2\times {10}^{-16}\times 3.35\times {10}^{-8}{\mathrm{cm}}^3\\ \therefore \text{Mass of the unit cell }=6\times \frac{\sqrt{3}}{4}\times 3.35\times d^2\times 2.25\times {10}^{-24}\mathrm{g}\text{ . }\\ \therefore 6\times \frac{\sqrt{3}}{4}\times 3.35\times 2.25\times {10}^{-24}\times d^2=12\times \frac{10}{6}\times {10}^{-24}\times 2\\ \therefore d^2=\frac{10}{3}\times 4\frac{1\times 2}{\sqrt{3}\times 3.35\times 2.25}=2.04265\text{ or }d=1.429\text{Å}\end{array}$