In a multi layered close-packed structure

In a closed packed structure

How are spheres arranged in first layer of cubic close-packed structures? How are successive layers of spheres placed above this layers?

Coordination number in a square close packed structure and hexagonal close packed structure respectively are

Why a hexagonal close-packed structure and a cubic close-packed structure for a given element would be expected to have the same density?

Why a hexagonal close-packed structure and a cubic close-packed structure for a given element would be expected to have the same density?

Why a hexagonal close-packed structure and a cubic close-packed structure for a given element would be expected to have the same density?