# Aluminium crystallises in a cubic close-packed structure. Its metallic radius is 125 pm.What is the length of the side of the unit cell?

$\begin{array}{1 1}354pm\\254pm\\554pm\\154pm\end{array}$

In ccp=fcc
$a=2\sqrt 2r$
$\Rightarrow 2\times 1.414\times 125$pm
$\Rightarrow 354$pm