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# Sodium crystallises in the cubic lattice and the edge of the unit cell is 430pm.Calculate the number of atoms in a unit cell.

$\begin{array}{1 1}2\\4\\5\\6\end{array}$

Density of sodium =$0.9623gcm^{-3}$
$N_A=6.023\times 10^{23}mol^{-1}$
$d=\large\frac{z\times M}{a^3\times N_A}$
$0.9623=\large\frac{z\times 23}{(430\times 10^{-10})^3\times 6.023\times 10^{23}}$
$z=\large\frac{0.9623\times (430)^3\times 6.023\times 10^{-7}}{23}$
$\Rightarrow z=2$