Question

Density of Li atom is $0.53$ g$/c{m}^3$. The edge length of Li is $3.5$ $\stackrel{o}{A}$. Find out the number of Li atoms in a unit cell. [$N_A=6.02\times {10}^{23}$ and $M=6.94$g $mo{l}^{-1}$]

• A. $2$
• B. $8$
• C. $4$
• D. $6$

Answer 1

Answer: (A)

$2$

$\rho =0.53$ $g/c{m}^3$

$a=3.5\mathring{A}$

$M_{Li}=6.49$ $gmo{l}^{-1}$

$Z=?$

$\rho =\frac{Z\times M_A}{N_A\times a^3}$

$0.53=\frac{Z\times 6.94}{6.023\times 42.815\times {10}^{23}\times {10}^{-24}}$

$⟹Z=2$

So, $2Li$ atoms are present in a unit cell.