Question

The density of KBr is $2.75$ g cm${}^{-3}$. The length of an edge of the unit cell is $654$ pm. To which type of cubic crystal does KBr belong?

• A. Simple cubic
• B. Body-centered cubic
• C. Face-centered cubic
• D. None of the above

Answer 1

Answer: (C)

Face-centered cubic

$d=\frac{ZM}{N_A\times V}$

$2.75=\frac{Z\times 119}{6.023\times {10}^{23}\times (0.654\times {10}^{-10}{)}^3}$

$z=\frac{2.75\times 6.023\times {10}^{23}\times (0.654\times {10}^{-10}{)}^3}{119}$

$Z=4$

$⟹$ The crystal type is face-centred cubic crystal.