Question

A metal crystallizes in two cubic phases, face centered cubic (fcc) and body centered cubic (bcc) whose unit cell length are $3.5\mathring{A}$ and $3.0\mathring{A}$ respectively. Calculate the ratio of density of fcc and bcc ?

• A. $2.6g/c{m}^3$
• B. $1.25g/c{m}^3$
• C. $3.25g/c{m}^3$
• D. $12.5g/c{m}^3$

Answer 1

The correct option is B $1.25g/c{m}^3$

$d=\frac{Z\times Mwt}{N_a\times a^3}$

$\therefore d\propto \frac{Z}{a^3}$ or $\frac{d_1}{d_2}=\frac{4\times 3^3}{2\times {3.5}^3}=1.25\frac{g}{c{m}^3}$