Which type of packing is involved in the above-mentioned figure?

2-D Hexagonal Close packing

If the arrangement of spheres in the first row is called ‘A’ type, the one in the second row is different and may be called ‘B’ type. When the third row is placed adjacent to the second in staggered manner, its spheres are aligned with those of the first layer. Hence this layer is also of ‘A’ type. The spheres of similarly placed fourth row will be aligned with those of the second row (‘B’ type). Hence this arrangement is of ABAB type.

In this arrangement there is less free space, and this packing is more efficient than the square close packing.

Each sphere is in contact with six of its Neighbours and the two-dimensional coordination number is 6.

The centres of these six spheres are at the corners of a regular hexagon, hence this packing is called two dimensional hexagonal close-packing.