Question

Ice crystallises in a hexagonal lattice having volume of the unit cell as 132 × 10^–24 cm³. If density is 0.92 g cm^–3 at a given temperature, then number of H₂O molecules per unit cell is –

• A. 1
• B. 2
• C. 3
• D. 4

Answer 1

Answer: (D)

4

Answer 2

$\frac{mass}{volume}$= d

Mass of n molecules of H₂O in hexagonal packing = $\frac{18n}{N_{0}}$ =

= $\frac{18n}{6.02 \times 10^{23} \times 132 \times 10^{- 24}}$= 0.92

\ n = $\frac{0.92 \times 6.02 \times 10^{- 1} \times 132}{18}$= 4