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# Aluminium crystallises in a cubic close-packed structure. Its metallic radius is 125 pm.How many unit cells are there in $1.00cm^3$ of aluminium?

$\begin{array}{1 1}2.26\times 10^{22}\\3.26\times 10^{22}\\1.26\times 10^{22}\\5.26\times 10^{22}\end{array}$

In ccp=fcc
$a=2\sqrt 2r=2\times 1.414\times 125$pm=354pm
Volume of one unit cell =$a^3=(354\times 10^{-8}cm)^3$
Unit cell in 1$cm^3=\large\frac{1}{(3.54\times 10^{-8})^3}$
$\Rightarrow 2.26\times 10^{22}$