Question

Which of the following compounds has hexagonal structure?
A.Diamond
B.$NaCl$
C.$KCl$
D.Graphite

Answer 1

Hint: To answer this question, you must be familiar with the structures of substances in the solid state. A substance in the solid state can have seven types of unit cells or structures, namely, cubic, tetragonal, orthorhombic, rhombohedral, hexagonal, monoclinic and triclinic. The compound with hexagonal structure is an allotrope of carbon.

Complete step by step answer:
Considering option A, we have diamonds.
Diamond is the most common allotrope of carbon. In diamond, each carbon is covalently bonded to four other carbon atoms in a tetrahedron or in a tetrahedral structure. The carbon atoms are arranged in the face centred cubic crystal lattice. It has a cubic unit cell or we can say that diamond has a cubic structure.
In option B, we have sodium chloride.
Sodium chloride is an ionic salt which exists as a crystalline salt. It is generally known as common salt. A unit cell of sodium chloride has a face centred cubic arrangement. The chloride ions occupy the corners of the unit cell while the sodium cations are present at the edge centres and the body center. It has a cubic structure.
In option C, we have potassium chloride.
Potassium chloride like sodium chloride has a face centred cubic lattice.
In option D, we have graphite.
It is another allotrope of carbon and is a good conductor of electricity. Graphite has a layered planar structure in which the carbon atoms are arranged in a hexagonal lattice in each layer.

Thus, the correct option is D.

Note:
Hexagonal close packing structure consists of alternating layers of particles arranged in hexagonal shape with an additional atom at the center which is in contact with all the six atoms. In the hexagonal unit cell, one cell comprises six effective atoms. It has a coordination number of 12.