The total number of tetrahedral voids in the face centred unit cell is ................

(a) 6 (b) 8 (c) 10 (d) 12

Answer (b). 8

The FCC unit cell contains 8 tetrahedral voids at the center of each 8 smaller cubes of a unit cell as shown below

Eight tetrahedral voids

per fcc unit cell

Each cube represented by numeric 1,2,3,4,5,6,7,8 center as shown above. Each cube contains one tetrahedral void at its body.

Number of atoms in fcc nuit cell = 4

Number of octahedral voids = 4

Number of tetrahedral voids = 8