1. A and B.
- A – Square close packed (scp) arrangement in two dimensions.
- B- Hexagonal close packed (hep) arrangement in two dimensions.
2. Explanation :
(a) A – Square close packed : (scp) arrangement in two dimensions – particles of the second row are arranged just below the first row. Similarly, particles of third row are arranged just below the particles of the second row and so on. Here vertical as well as horizontal alignment is possible. In this arrangement each particle is in direct contact with four other particles and the coordination number is 4.
(b) B- Hexagonal close packed : (hep) arrangement in two dimensions – In this arrangement, particles of second row are arranged in the depressions of the particles of the first row. Similarly the particles of the third row are arranged in the depressions of the particles of the second row. In this arrangement, each particle is in direct contact with six other particles and the coordination number is 6.