An element  M crystallises in a body centred cubic unit cell with a cell edge of 300 pm . The density of the element is 6.0 g cm^-3. The number of atoms present in 180 g of the element is ___________$\times$10²³

M is body centred cubic ,$\therefore$ Z=2 

Let mass of atom of M is A

Edge lenght  = 300 pm 

Density  = 6g/cm³ 

$$\begin{gathered} \therefore 6g/c{m}^3=\frac{Z\times A}{{\left(300\times {10}^{-10}\right)}^3}=\frac{2\times A}{27\times {10}^{-24}} \\ A=81\times {10}^{-24}g \\ \therefore Atomic mass =48.6g \\ \therefore Mole in 180g \frac{180}{48.6}=3.7 moles \\ Atoms of M = 3.7\times 6\times {10}^{23} \\ =22.22\times {10}^{23} \end{gathered}$$