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

The correct option is D In this arrangement spheres of the fourth layer are exactly aligned with those of the first layer.

Hexagonal close packing can be arranged by two layers A and B one over another which can be diagrammatically represented as above figure.

Here, we can see easily that 1st layer and 4th layer are not exactly aligned.

Coordination no. of an atom in hcp is 12, packing fraction of hcp is 74%.

Tetrahedral voids of the second layer are covered by the spheres of the third layer.

Thus, statement (D) is not correct while other statements (A), (B) and (C) are true.

Hence, Option "D" is the correct answer.