The elemental composition of diamond is

Diamond is a solid form of the element carbon with its atoms arranged in a crystal structure known as a diamond cubic lattice. It is one of the most well-known allotropes of carbon, alongside graphite and fullerenes.

• Chemical Structure: In a diamond, each carbon atom is joined to four other carbon atoms by strong covalent bonds in a rigid tetrahedral structure. This arrangement makes it the hardest known natural substance.
• Elemental Purity: Chemically, a diamond is composed entirely of carbon atoms. While natural diamonds may contain minute trace impurities (such as nitrogen or boron) that influence their color, their fundamental elemental identity remains pure carbon.
• Distinction: Unlike hydrocarbons (which contain hydrogen) or oxides, diamond does not contain other elements as part of its basic chemical formula.

Thus, the elemental composition of diamond is pure carbon, confirming Option C as the correct answer.