Calculate the number of atoms in a fcc unit cell.

Explanation

(i) A face centered cubic lattice has 4 atoms per unit cell.
(ii) The lattice has 8 atoms in the corners ( `N_(c )` ) and 6 atoms on the faces `( N_(f))` ( one on each face )
Contribution by atoms on the corners to unit cell `= ( N_( c ))/( 8) =( 8)/( 8) = 1 `
Contribution by atoms on the faces to unit cell `= ( N_(f))/( 2) = ( 6)/( 2) = 3`
`:.` The number of atoms per unit cell in fcc `= ( N_(c ))/(8) + ( N_(f))/( 2) = ( 8)/( 8) + ( 6)/(2) = 1+ 3= 4`