In diamond, a group of five carbon atoms with one at the center is called what?

• A. A four-faced polyhedron in general.
• B. A pentagonal arrangement of atoms in a lattice.
• C. A single carbon atom at the center of the diamond.
• D. In diamond, a group of five carbon atoms with one at the center.

Answer: (D)

In diamond, each carbon atom sits at the center of a tetrahedron formed by four neighboring carbons. If you consider that central atom plus its four surrounding atoms, you get a five-atom cluster. Describing it as a group of five carbon atoms with one at the center directly matches this local tetrahedral coordination in the diamond lattice. The other descriptions don’t fit: a four-faced polyhedron describes just the outer tetrahedron, not the five-atom cluster; a pentagonal arrangement implies a five-atom arrangement around in a pentagon, which isn’t how the neighbors are positioned tetrahedrally; and stating only a central atom misses the surrounding atoms. So this descriptive five-atom cluster is the correct way to name the described arrangement.