Question

The arrangement of the first two layers, one above the other, in the hcp and ccp arrangement is:

• A. Partly same
• B. Nothing definite
• C. Different from each other
• D. Exactly the same in both cases.

Answer 1

The correct option is D

Exactly the same in both cases.

In both the hexagonal close packing (HCP) and cubic close packing (CCP) systems, each sphere is surrounded by twelve other spheres.

12 Co-ordination number in HCP & CCP structure

The arrangement of the first two layers, one above the other, in the hexagonal close packing (hcp) and cubic close packing (ccp) is exactly the same in both cases. It is an AB type

Explanation for incorrect option:

• The arrangement of the third layer in hcp is ABA type.
• The overall arrangement becomes ABAB type.
• The arrangement of the third layer one above the other in ccp is ABC type.
• Therefore the overall arrangement becomes ABCABC type

Hence, Option(D) is correct.