Assertion: In HCP structure, Ist and IIIrd layer coincides.
Reason: Coordination number in HCP lattice structure is 8.
Answer & explanation
Correct answer: option 3
The correct answer is option 3. Assertion is correct statement, but reason is wrong statement.
Hexagonal closed packed structure (HCP)
In this type of structure, the spheres of the third layer are exactly aligned with those of the first layer. Thus, the pattern of spheres is repeated in alternate layers. This pattern is often written as ABAB ....... pattern. This structure is called hexagonal close packed (hcp) structure. This sort of arrangement of atoms is found in many metals like magnesium and zinc.
This type of close packing is highly efficient and 74% space in the crystal is filled. Each sphere is in contact with twelve spheres. Thus, the coordination number is 12 in this structure.
