Ncert Exercises & Solutions

The incorrect statement among the following regarding hexagonal close packing is:

1.	The coordination number is 12.
2.	It has 74% packing efficiency.
3.	Tetrahedral voids of the second layer are covered by the spheres of the third layer.
4.	In this arrangement, spheres of the fourth layer are exactly aligned with those of the first layer.

HINT: In HCP, packing efficiency is 74%

Explanation:

Hexagonal close-packing can be arranged by two layers A and B one over other which can be diagrammatically represented as :

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

Thus, statement (4) is not correct while other statements (1), (2), and (3) are true.