Question

Which of the following statements is not true about the hexagonal close packing?

• A. The coordination number is 12.
• B. It has 74% packing efficiency.
• C. Tetrahedral voids of the second layer are covered by the spheres of the third layer.
• D. In this arrangement spheres of the fourth layer are exactly aligned with those of the first layer.

Answer 1

Answer: (D)

In this arrangement spheres of the fourth layer are exactly aligned with those of the first layer.

Answer 2

When third layer is placed over the second layer and all tetrahedral voids are covered by the spheres of the third layer then in this case, the spheres of the third layer are exactly aligned with those of the fist layer. (ABAB…….. pattern). This structure is called hexagonal close packed (hcp) structure.