A crystalline solid of a pure substance has a face-centred 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 256g of the crystal is `N xx 10^(24)`. The value of `N` is

Answer

c

Explanation

`p ( Z xx M)/( a^(3) xx N_(0) xx 10^(-30)`
Where a is in pm and M in g ` Mol^(-1)`
` 8 = ( 4 xx M)/((400)^(3) xx 6 xx 10^(23) xx 10^(-30))) or M = 76.8`
Moles in 256 g = ` 256/76.8 = 3.33`
No, of atoms = ` 3.33 xx 6 xx 10^(23)`
`= 2xx 10^(24)`