Question

If ${}^{\prime }{Z}^{\prime }$ is the number of atoms in the unit cell that represents the closest packing sequence $-ABCABC-$, the number of tetrahedral voids in the unit cell is equal to:

• A. $Z$
• B. $2Z$
• C. $Z/2$
• D. $Z/4$

Answer 1

The correct option is B $2Z$

If $Z$ is the number of atoms in the unit cell that represents the closest packing sequence - ABCABC-, the number of tetrahedral voids in the unit cell is equal to $2Z$.
ABCABC type packing is present in FCC unit cell.
For an FCC unit cell tetrahedral voids are present at a distance of d/4 from all the corners on each body diagonal where d is the length of the body diagonal.