Question

Which of the following statements regarding close packing is correct?

• A. In 1D, efficient packing is when spheres does not touch each other.
• B. In 2-D, ABAB... type arrangement gives square close packing
• C. The coordination number of square close packing in 2-D is 8
• D. Particles are assumed as identical sphere in measuring packing efficiency

Answer 1

The correct option is D Particles are assumed as identical sphere in measuring packing efficiency

In 1-D closed packing, the closest efficient packing is when the spheres just touch each other.
Thus, statement (a) is wrong.

Square close packing in 2D:
Here, the second row of spheres is placed adjacent to the first row so that the spheres in the two rows are aligned horizontally, as well as, vertically. Thus, it gives AAA type arrangement.
Thus, statement (b) is incorrect.

Each sphere touches 4 other neighbours in scp. Thus, its coordination number is 4.
The centres of the neighbouring spheres joins to form a square.​​ So, the packing is known as square close packing in 2-D.​
Thus, statement (c) is wrong.


In crystalline solids, the constituent particles are close-packed, leaving very less vacant space. In measuring efficiency of packing, particles are assumed as sphere of identical size.
Thus, statement (d) is correct.