Ice crystallises in a hexagonal lattice having a volume of the unit cell as $132\times {10}^{-24}{ \mathrm{cm}}^3$ If density of ice at the given temperature is . If density of ice at the given temperature is 0.92 g cm^–3, then number of H₂O molecules per unit cell is

Volume =132×10⁻²⁴ cm³

Density  =0.92 g cm⁻³

Mass of the unit cell = Volume × Density

 =132×10⁻²⁴×0.92 =121.44×10⁻²⁴ g

Molar mass of water =18.02 g mol⁻¹

Number of moles of water =$\frac{121.44\times {10}^{-24}}{18.02 }$ mol

Number of molecules =6.739×10⁻²⁴×6.023×10²³ molecules per mole =4.05 molecules =4 molecules approximately