The well know mineral flourite is chemically calcium fluoride. It is a well known fact that in one unit cell of this mineral, there are four `Ca^(2+)` ions and eight `F^(-)` ions and `Ca^(2+)` ions are arranged in f.c.c. lattice. The `F^(-)` ions fill all the tetrahedral holes in the face centred cubic lattice of `Ca^(2+)` ions. The edge length of the unit cell is `5.46xx10^(-8)` cm. The density of the solid is `3.18"g cm"^(-3)`. Use this information to calculate Avogadro's number (Molar mass of `CaF_(2)=78.0"g mol"^(-1)`)

Explanation

Density = `(Z xx M)/(a^3 xx N_A)`
`3.18 g cm^(-3) = (4 xx 78.08 g mol^(-1))/((5.46 xx 10^(-8) cm)^(3) xx N_A)`
`:. N_A = 6.02 xx 10^(23)`.