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A crystalline solid of a pure substance has a face-centered cubic structure with a cell edge of 400 pm. If the density of the substance in the crystal is 8 g cm^-3 , then the number of atoms present in 256 g of the crystal is N × 10²⁴.  The value  of N is 

Answer:

Explanation:

Density (ρ )=  $8=\frac{4\times M}{N_{A}(4\times 10^{-8}cm)^{3}}$

                         M= 128 × 10^-24 N_A

$\Rightarrow$     No of atoms=  $\frac{256}{M}\times N_{A}$

    =   $\frac{256}{128\times 10^{-24}N_{A}}\times N_{A}$

   =2 × 10²⁴