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** Q 2641578423. ** The well known mineral fluorite is chemically calcium fluoride. It is known that in one unit cell of this mineral, there are 4 `Ca^(2+)` ions and 8 `F^-` ions and that `Ca^(2+)` ions are arranged in fcc lattice. The `F^-` ions fill all the tetrahedral holes in the face centred cubic lattice of `Ca^(2+)` ions. The edge of the unit cell is `5.46 xx 10^-8` cm in length. The density of the solid is 3.18 g `cm^-3`. Use this information to calculate Avogadro's number (Molar mass of `CaF_2 = 78.08 g mol^-1`)

**CBSE-12th 2010 **