Question

An element X(At. wt.=80 g/mol) having fcc structure,calculate no. of unit cells in 8gm of X :

Answer 1

As we know,

Number of unit cells= $\frac{Weight}{Molecularweight}\times \frac{N_A}{Z}$

$\Rightarrow \frac{8}{80}\times \frac{N_A}{4}$ [$Z$ for fcc= $4$]

$=\frac{N_A}{40}\Rightarrow \frac{6.023\times {10}^{23}}{40}=1.55\times {10}^{22}$