Question

A metal crystallizes with hcp packing. The total number of voids, total number of tetrahedral voids and total number of octahedral voids are shown as A, B and C respectively. A, B and C in 0.25 moles of metal are respectively ($N_A$ = Avogadro number).

• A. 0.5 $N_A$, 0.25 $N_A$, 0.75 $N_A$
• B. 0.75 $N_A$, 0.25 $N_A$, 0.5 $N_A$
• C. 0.5 $N_A$, 0.75 $N_A$, 0.25 $N_A$
• D. 0.75 $N_A$, 0.5 $N_A$, 0.25 $N_A$

Hint:

Always remember void formulas for close-packed structures: tetrahedral voids = 2 × atoms, octahedral voids = atoms.

Answer 1

The Correct Option is D

For hcp and ccp structures: 
Total voids = 0.75 $N_A$, Tetrahedral voids = $N_A$, and Octahedral voids = 0.5 $N_A$. 
For 0.25 mol metal: A = 0.75 × 0.25 $N_A$, B = 0.5 × 0.25 $N_A$, C = 0.25 × 0.25 $N_A$.