`"Molar mass of solid = 259.8 g mol"(-1)`
A solid crystallises in hexagonal lattice as shown in above figure. Density of the solid is 5 g/cm3. How many molecules are their in the given unit cell? (Avogadro's number `= 6.023 xx 10^(23)`) 

Answer

2

Explanation

Volume of the unit cell `=x^(2)xxsin 60^(@)xxy=173.2xx10^(-24)cm^(3)`
mass of the unit cell `=173.2xx10^(2)xxsin60^(@)xxy=173.2xx10^(-24)cm^(3)`
mass of the unit cell `=173.2xx10^(-24)xx5xx6xx10^(23)=519.6gm` no. of molecules in the given unit cell `=(519.6)/(259.8)=2`