Question

An element (atomic mass $100 \,g /\, mol$ ) having $BCC$ structure has unit cell edge $400\, pm$. The density of element is (No. of atom in $BCC ( Z )=2$ ).

• A. $10.376\, g/cm^3$
• B. $5.1888 \,g/cm^3$
• C. $7.289\, g/cm^3$
• D. $2.144 \,g/cm^3$

Answer 1

Answer: (B)

$5.1888 \,g/cm^3$

Answer 2

No. of atoms per unit cell in $b.c.c.$ lattice $(n) = 2$

Density, $d = \frac{n \times M}{a^3 \times N_A}$
$= \frac{2\times 100}{(4\times 10^{-8}\,cm)^3 \times 6.02 \times 10^{23}}$
$= \frac{200}{38.528}$
$= 5.19\,g/cm^3$.