Question

When heated above ${916}^{\circ }C$, iron changes its bcc crystalline form to fcc without the change in the radius of atom. The ratio of density of the crystal before heating and after heating is :

• A. $1.069$
• B. $0.918$
• C. $0.725$
• D. $1.231$

Answer 1

The correct option is B $0.918$

The ratio of density of the crystal before heating and after heating is
$\frac{d_1}{d_2}=\frac{\frac{z_{1}M}{V_1{N}_0}}{\frac{z_{2}M}{V_2{N}_0}}=\frac{\frac{z_1}{V_1}}{\frac{z_2}{V_2}}=\frac{\frac{2}{(4r/\sqrt{3}{)}^3}}{\frac{4}{(2\sqrt{2}{)}^3}}=0.918$

option B is correct.