Question

An element $A$ crystallises in fcc structure. $200g$ of this element has $4.12\times {10}^{24}$ atoms. The density of $A$ is $7.2gc{m}^{-3}$. Calculate the edge length of the unit cell.

• A. $26.97\times {10}^{-24}cm$
• B. $299.9pm$
• C. $5\times {10}^{-12}cm$
• D. $2.99cm$

Answer 1

The correct option is B $299.9pm$

$Fcc$ No of atoms $=4$
Given $200\to 4.12\times {10}^{24ar}$
$\therefore 9$ atoms will to $\frac{200\times 4}{4.12\times {10}^{24}g}$
& We know, density $\frac{m}{V}$
$\therefore 7.2=\frac{200\times 4}{4.12\times {10}^{24}}$
$\therefore a=300pm$ approx