Which crystalline structure is exemplified by zinc and cadmium?

The crystalline structure exemplified by zinc and cadmium is the Face Centred Cubic (FCC) structure. In this arrangement, atoms are located at each of the corners and the centers of all the faces of the cube. This structure allows for a high packing efficiency, where the atoms are closely packed, resulting in a dense arrangement.

In the case of zinc and cadmium, they exhibit a unique characteristic of the FCC structure known as the "Laves phase" due to their coordination number of 12, allowing for efficient packing and stability in their metallic forms. This contributes to their desirable properties such as ductility and strength.

Both metals can also transition into a hexagonal close-packed structure under certain conditions; however, at standard conditions, their dominant crystalline structure is indeed FCC, thus making it the correct choice.