Calculate the approximate number of unit cells present in 1 g of gold. Given that gold cyrstallises in a face centred cubic lathce (Given atomic mass of gold = 197 u).

Options

A. `6.02xx10^(23)`
B. `7.64xx10^(20)`
C. `3.82xx10^(20)`
D. `15.28xx10^(20)`

Answer

B

Explanation

1 Mole of gold = 197 g `mol^(-1)=6.02xx10^(23)` atoms
`:.` 1g gold `=(6.02xx10^(23))/(197)` atoms
As fcc contains 4 atoms per unit cell, therefore,
number of unit cells `=(6.02xx10^(23))/(197xx4)=7.64xx10^(20)`