Question

An element crystallising in body centred cubic lattice has an edge length of 500 pm. If its density is 4 g $c{m}^{-3}$, the atomic mass of the element $($in g $mo{l}^{-1})$ is
(consider $N_A=6\times {10}^{23}$)

• A. 100
• B. 250
• C. 125
• D. 150

Answer 1

The correct option is D 150

For $\text{bcc},Z=2$
$d=\frac{Z\times M}{N_A\times a^3}\Rightarrow M=\frac{d\times N_A\times a^3}{Z}$
$\therefore M=\frac{4\times 6\times {10}^{23}\times (500\times {10}^{-10}{)}^3}{2}$
$M=\frac{4\times 6\times {10}^{23}\times 125\times {10}^{-24}}{2}M=150{\text{g mol}}^{-1}$