Ice crystallises in hexagonal lattice having volume of unit cell is `132times10^(-24)cm^(3)`.If density is 0.92g `cm^(3)`at a given temperature, then number of water molecules per unit cell is

Options

A. 1
B. 2
C. 3
D. 4

Answer

D

Explanation

Density `(rho)=("Mass")/("Volume")`
Mass of n molecules of `H_(2)O`
in hcc packing `=(18n)/("No")=((18g " mol"^(-1))xxn)/((6.022xx10^(23)" mol"^(-1)))`
`(0.92 g " cm" ^(-3))=((18g " mol"^(-1))xxn)/((6.022xx10^(23)" mol"^(-1))xx(132xx10^(-24)cm^(3)))`
`n=((0.92 g cm^(3))xx(6.022xx10" mol"^(-1))xx(132xx10^(-24)cm^(3)))/((18g " mol"^(-1)))=4`