# The density of chromium is 7.2 gm cm. And crystallises in a body centered cu ic lattice with edge length 290 pm. The num of atoms present in 30.0 gm of the sample.

Dear Student,
d= 7.2 gm/cm3, a=290 pm
Bcc lattice so Z=2  , m=3 gm
$d=\frac{Z×m}{{a}^{3}×{N}_{A}}$
$7.2=\frac{2×3}{\left(298×{10}^{-10}{\right)}^{3}×N}$
N=$\frac{2×3}{7.2×\left(298×{10}^{-10}{\right)}^{3}}$
number of atoms or N = $3.14×{10}^{22}$

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